common/lcd: add protection from null bmp pointer

If the bmp pointer is null then U-Boot will get stuck when trying
to load the image.
What's worse, it will get stuck before the U-Boot shell becomes
available to the user, thus making it difficult to correct the
situation.

To protect from the above scenario, check if the pointer is valid.

Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>

common/lcd.c

@@ -674,7 +674,7 @@ int lcd_display_bitmap(ulong bmp_image, int x, int y)
 	unsigned long pwidth = panel_info.vl_col;
 	unsigned colors, bpix, bmp_bpix;
 
-	if (!((bmp->header.signature[0] == 'B') &&
+	if (!bmp || !((bmp->header.signature[0] == 'B') &&
 		(bmp->header.signature[1] == 'M'))) {
 		printf("Error: no valid bmp image at %lx\n", bmp_image);