Fix fpcrtl_strappendA, which cut last char from UserPathPrefix
leading to PHYSFS_setWriteDir fail with 'File not found' error,
which led to lack of writing dir and logFile handle being nil,
which led to crash on attempt to write to (absent) log file
SDL blit wraps at 16,384 - not the first time that routine has disappointed us.
Fixes crash Wuzzy and I were encountering in debian fpc 2.6.2 and 3.0.0 after the addition of the uPhysFSLayer dependency to uUtils in
rcac74d9075be