QTemporaryFile bug regarding filename generation

QTemporaryFile contains a subtle bug regarding filename generation on Windows, which can cause it to fail randomly under certain circumstances.
The bug has occured on our workstation twice.

Background:

On Windows getpid() is implemented in CRT as follows:

int _getpid (void)
{
return (int)GetCurrentProcessId();
}

Please note the signature of GetCurrentProcessId() :

DWORD WINAPI GetCurrentProcessId(void);

Therefore due to the aforementioned cast of DWORD to int, getpid() can return values that are negative on Windows

Please note how the _gettemp() function threats the output of getpid() in this formula:

while (trv >= path && *trv == 'X' && pid != 0)

In case of negative pid, trv array will be filled with non-digit ascii characters.

The fix is simple - before the loop check if pid is negative and make it non-negative.