Fix "result of 32-bit shift implicitly converted to 64 bits" on WNT x64

On Windows x64 long is only 32-bit (while on other x64 platforms it is
typically 64-bit), but sal_uLong is not a typedef for unsigned long, but
rather for sal_uIntPtr, which in turn is large enough to take recast
pointer values (i.e., always 64-bit on 64-bit platforms).
sal_uLong was introduced as a "temporary helper type" to ease transition
from the old tools/solar.h types ("ULONG" etc.), but in the long run it
should be remove from the code base, and places that now use sal_uLong
analysed to use more appropriate types.

As short term solution, cast to sal_uLong fixes it.

Change-Id: I2169b7858517313616007a8fb2acc5c7d0487719
Reviewed-on: https://gerrit.libreoffice.org/13232
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>