Fix bmp RLE "bug" and add invalid image test to CodexTest

src/codec/SkBmpRLECodec.h

Index: src/codec/SkBmpRLECodec.h
diff --git a/src/codec/SkBmpRLECodec.h b/src/codec/SkBmpRLECodec.h
index f1f1ae97d8b2ba596c781592d8315935537dc7ec..ee8989be64d78861b2c62a9ea7b02f86d75f64d0 100644
--- a/src/codec/SkBmpRLECodec.h
+++ b/src/codec/SkBmpRLECodec.h
@@ -56,6 +56,15 @@ private:
     bool initializeStreamBuffer();
 
     /*
+     * Before signalling kIncompleteInput, we should attempt to load the
+     * stream buffer with additional data.
+     *
+     * @return the number of bytes remaining in the stream buffer after
+     *         attempting to read more bytes from the stream
+     */
+    size_t checkForMoreData();
+
+    /*
      * Set an RLE pixel using the color table
      */
     void setPixel(void* dst, size_t dstRowBytes,