PlayHavenRequest fix for Charset.forName crash

Charset class seems not to be multi-thread safe, so fixing it by getting the Charset object on the main thread.
More info (mentioning a different Charset class method, but still valid) here: https://code.google.com/p/android/issues/detail?id=42769

Observed example crashlog:

03-31 10:25:27.068: A/NmgBreakPad(17396): Fatal signal 11 (SIGSEGV) at 0x00000014 (code=1), thread 17829 (Thread-3307)
03-31 10:25:27.068: A/NmgBreakPad(17396): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
03-31 10:25:27.068: A/NmgBreakPad(17396): Build fingerprint: 'google/nakasi/grouper:4.2.2/JDQ39/573038:user/release-keys'
03-31 10:25:27.068: A/NmgBreakPad(17396): Revision: 'google/nakasi/grouper:4.2.2/JDQ39/573038:user/release-keys'
03-31 10:25:27.068: A/NmgBreakPad(17396): pid: 20, tid: 17829, name: Thread-3307 >>  <<
03-31 10:25:27.068: A/NmgBreakPad(17396): signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 00000014
03-31 10:25:27.068: A/NmgBreakPad(17396):     r0 00000000  r1 00000000  r2 00000001  r3 00000019
03-31 10:25:27.068: A/NmgBreakPad(17396):     r4 00000000  r5 00000000  r6 728d4ac0  r7 704ccbc0
03-31 10:25:27.068: A/NmgBreakPad(17396):     r8 728d4bfc  r9 406b030c  10 67e43a10  fp 728d4c8c
03-31 10:25:27.068: A/NmgBreakPad(17396):     ip 00000000  sp 728d4a78  lr 40641079  pc 40600378  cpsr 20000030
03-31 10:25:27.068: A/NmgBreakPad(17396):     d0 00000000  d1 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d2 00000000  d3 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d4 00000000  d5 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d6 00000000  d7 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d8 00000000  d9 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d10 00000000  d11 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d12 00000000  d13 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d14 00000000  d15 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d16 00000000  d17 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d18 00000000  d19 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d20 00000000  d21 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d22 00000000  d23 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d24 00000000  d25 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d26 00000000  d27 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d28 00000000  d29 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     d30 00000000  d31 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396):     scr 00000000
03-31 10:25:27.068: A/NmgBreakPad(17396): backtrace:
03-31 10:25:27.068: A/NmgBreakPad(17396):          #00  pc 00046378  /system/lib/libicuuc.so  (icu_48::UnicodeSet::compact()+3)
03-31 10:25:27.068: A/NmgBreakPad(17396):          #01  pc 00087075  /system/lib/libicuuc.so
03-31 10:25:27.068: A/NmgBreakPad(17396):          #02  pc 0007d079  /system/lib/libicuuc.so
03-31 10:25:27.068: A/NmgBreakPad(17396):          #03  pc 0007d831  /system/lib/libicuuc.so
03-31 10:25:27.068: A/NmgBreakPad(17396):          #04  pc 000189c5  /system/lib/libjavacore.so
03-31 10:25:27.068: A/NmgBreakPad(17396):          #05  pc 0001e290  /system/lib/libdvm.so  (dvmPlatformInvoke+112)
03-31 10:25:27.068: A/NmgBreakPad(17396):          #06  pc 0004d411  /system/lib/libdvm.so  (dvmCallJNIMethod(unsigned int const*, JValue*, Method const*, Thread*)+396)
03-31 10:25:27.068: A/NmgBreakPad(17396):          #07  pc 000276a0  /system/lib/libdvm.so
03-31 10:25:27.068: A/NmgBreakPad(17396):          #08  pc 0002b57c  /system/lib/libdvm.so  (dvmInterpret(Thread*, Method const*, JValue*)+184)
03-31 10:25:27.068: A/NmgBreakPad(17396):          #09  pc 0005fc31  /system/lib/libdvm.so  (dvmCallMethodV(Thread*, Method const*, Object*, bool, JValue*, std::__va_list)+272)
03-31 10:25:27.068: A/NmgBreakPad(17396):          #10  pc 0005fc5b  /system/lib/libdvm.so  (dvmCallMethod(Thread*, Method const*, Object*, JValue*, ...)+20)
03-31 10:25:27.068: A/NmgBreakPad(17396):          #11  pc 000547d7  /system/lib/libdvm.so
03-31 10:25:27.068: A/NmgBreakPad(17396):          #12  pc 0000e3d8  /system/lib/libc.so  (__thread_entry+72)
03-31 10:25:27.068: A/NmgBreakPad(17396):          #13  pc 0000dac4  /system/lib/libc.so  (pthread_create+160)
03-31 10:25:27.068: A/NmgBreakPad(17396): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***