glsl/blob: Return false from ensure_can_read on overrun

Otherwise, if you have a large read fail and then try to do a small
read, the small read may succeed even though it's at the wrong offset.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Cc: mesa-stable@lists.freedesktop.org

src/compiler/glsl/blob.c

@@ -207,6 +207,9 @@ blob_reader_init(struct blob_reader *blob, uint8_t *data, size_t size)
 static bool
 ensure_can_read(struct blob_reader *blob, size_t size)
 {
+   if (blob->overrun)
+      return false;
+
    if (blob->current < blob->end && blob->end - blob->current >= size)
       return true;