PyErr_ProgramText(): Grrrrrr.

In a Windows debug build, trying to open a file using
an empty string as the name causes assertion death
inside MS's C runtime code.  We probably need to worm
around that in many places.  I'm worming around it here
to stop the new test_with.py from assert-dying in the
Windows debug build (it calls compile() with an empty
string for "the file name", which indirectly leads to
C-level code in Python trying to fopen("", "r")).

Python/errors.c

@@ -738,7 +738,7 @@ PyErr_ProgramText(const char *filename, int lineno)
 	int i;
 	char linebuf[1000];
 
-	if (filename == NULL || lineno <= 0)
+	if (filename == NULL || *filename == '\0' || lineno <= 0)
 		return NULL;
 	fp = fopen(filename, "r" PY_STDIOTEXTMODE);
 	if (fp == NULL)