Fix gcc (4.0.x) warning about use of uninitialized variables.

(PyMarshal_ReadShortFromFile() is only used in zipimport.c, I don't believe
the extra initializations will matter one way or another.)

Python/marshal.c

@@ -885,8 +885,9 @@ int
 PyMarshal_ReadShortFromFile(FILE *fp)
 {
 	RFILE rf;
+	assert(fp);
 	rf.fp = fp;
-	rf.strings = NULL;
+	rf.strings = rf.end = rf.ptr = NULL;
 	return r_short(&rf);
 }