LibGfx/TGA: Move a variable closer to its use

No behavior change.

Userland/Libraries/LibGfx/ImageFormats/TGALoader.cpp

@@ -76,9 +76,9 @@ IntSize TGAImageDecoderPlugin::size()
 
 static ErrorOr<void> ensure_header_validity(TGAHeader const& header, size_t whole_image_stream_size)
 {
-    auto bytes_remaining = whole_image_stream_size - sizeof(TGAHeader);
     if ((header.bits_per_pixel % 8) != 0 || header.bits_per_pixel < 8 || header.bits_per_pixel > 32)
         return Error::from_string_literal("Invalid bit depth");
+    auto bytes_remaining = whole_image_stream_size - sizeof(TGAHeader);
     if (header.data_type_code == TGADataType::UncompressedRGB && bytes_remaining < static_cast<u64>(header.width) * header.height * (header.bits_per_pixel / 8))
         return Error::from_string_literal("Not enough data to read an image with the expected size");
     return {};