LibGfx: Always compute the DIB mask shifts and sizes if needed

The pixel decoding logic later on assumes that if we have DIB masks,
we also have shifts and sizes, so we should make sure they are
always computed.

Found by oss-fuzz: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=28237

Libraries/LibGfx/BMPLoader.cpp

@@ -336,7 +336,7 @@ static u32 int_to_scaled_rgb(BMPLoadingContext& context, u32 data)
     return color;
 }
 
-static void populate_dib_mask_info(BMPLoadingContext& context)
+static void populate_dib_mask_info_if_needed(BMPLoadingContext& context)
 {
     if (context.dib.info.masks.is_empty())
         return;
@@ -439,8 +439,6 @@ static bool set_dib_bitmasks(BMPLoadingContext& context, Streamer& streamer)
         context.dib.info.masks.append({ 0x7c00, 0x03e0, 0x001f });
         context.dib.info.mask_shifts.append({ 7, 2, -3 });
         context.dib.info.mask_sizes.append({ 5, 5, 5 });
-
-        populate_dib_mask_info(context);
     } else if (type == DIBType::Info && (compression == Compression::BITFIELDS || compression == Compression::ALPHABITFIELDS)) {
         // Consume the extra BITFIELDS bytes
         auto number_of_mask_fields = compression == Compression::ALPHABITFIELDS ? 4 : 3;
@@ -450,12 +448,9 @@ static bool set_dib_bitmasks(BMPLoadingContext& context, Streamer& streamer)
                 return false;
             context.dib.info.masks.append(streamer.read_u32());
         }
-
-        populate_dib_mask_info(context);
-    } else if (type >= DIBType::V2 && compression == Compression::BITFIELDS) {
-        populate_dib_mask_info(context);
     }
 
+    populate_dib_mask_info_if_needed(context);
     return true;
 }