restore minui support for paletted images with < 8 bits

The PNG image loaders should support images that use palettes
requiring fewer than 8 bits.

Change-Id: Ibcb0ff6f04aea8de54b03c0efa7a79e9b3635146
diff --git a/minui/resources.c b/minui/resources.c
index a0c621b..2bae4de 100644
--- a/minui/resources.c
+++ b/minui/resources.c
@@ -101,7 +101,7 @@
     } else if (bit_depth <= 8 && *channels == 1 && color_type == PNG_COLOR_TYPE_GRAY) {
         // 1-, 2-, 4-, or 8-bit gray images: expand to 8-bit gray.
         png_set_expand_gray_1_2_4_to_8(*png_ptr);
-    } else if (bit_depth == 8 && *channels == 1 && color_type == PNG_COLOR_TYPE_PALETTE) {
+    } else if (bit_depth <= 8 && *channels == 1 && color_type == PNG_COLOR_TYPE_PALETTE) {
         // paletted images: expand to 8-bit RGB.  Note that we DON'T
         // currently expand the tRNS chunk (if any) to an alpha
         // channel, because minui doesn't support alpha channels in