Fix broken buflib_handle check in backdrop settings loader

The logic was messed up and always evaluated to true
if buflib_handle is non-zero.

Thanks to JdGordon for verifying the change.

cppcheck reported:
[rockbox/apps/gui/skin_engine/skin_backdrops.c:262]: (warning) Comparison of a boolean expression with an integer other than 0 or 1.

Change-Id: Ib52a73e0a6a2017a631e2dec19b638a2974dab83
text_viewer plugin: Fix two out-of-bounds buffer accesses

Test code:
--------------
int main(void)
{
    static unsigned short extra_spaces[] = { 0, 0x3000 };
    return sizeof(extra_spaces);
}
--------------

-> returns four instead of two.

cppcheck reported:
[rockbox/apps/plugins/text_viewer/tv_text_processor.c:180]: (error) Array 'break_chars[27]' acces
sed at index 53, which is out of bounds.
[rockbox/apps/plugins/text_viewer/tv_text_processor.c:195]: (error) Array 'extra_spaces[2]' acces
sed at index 3, which is out of bounds.

Change-Id: I66c305cc5c99e59e7c8e0aa9c86cecbe293ff037