handle negative return values

do not pass negative values to malloc

do not pass negative values to strerror

do not pass negative values to ftruncate

do not pass negative values to fclose

Change-Id: I79ebef4e22edd14343ebeebb2ef8308785064fe8

lib/krb5/store_stdio.c

@@ -137,6 +137,8 @@ stdio_trunc(krb5_storage * sp, off_t offset)
     if (fflush(F(sp)) == EOF)
         return errno;
     tmpoff = ftello(F(sp));
+    if (tmpoff < 0)
+	return errno;
     if (tmpoff > offset)
 	tmpoff = offset;
     if (ftruncate(fileno(F(sp)), offset) == -1)