Fix compiler warnings for different signed comparisons

Backends/RmlUi_Renderer_GL2.cpp

@@ -309,7 +309,7 @@ Rml::TextureHandle RenderInterface_GL2::LoadTexture(Rml::Vector2i& texture_dimen
 
 Rml::TextureHandle RenderInterface_GL2::GenerateTexture(Rml::Span<const Rml::byte> source, Rml::Vector2i source_dimensions)
 {
-	RMLUI_ASSERT(source.data() && source.size() == source_dimensions.x * source_dimensions.y * 4);
+	RMLUI_ASSERT(source.data() && source.size() == size_t(source_dimensions.x * source_dimensions.y * 4));
 
 	GLuint texture_id = 0;
 	glGenTextures(1, &texture_id);

Backends/RmlUi_Renderer_GL3.cpp

@@ -1272,7 +1272,7 @@ Rml::TextureHandle RenderInterface_GL3::LoadTexture(Rml::Vector2i& texture_dimen
 
 Rml::TextureHandle RenderInterface_GL3::GenerateTexture(Rml::Span<const Rml::byte> source_data, Rml::Vector2i source_dimensions)
 {
-	RMLUI_ASSERT(source_data.data() && source_data.size() == source_dimensions.x * source_dimensions.y * 4);
+	RMLUI_ASSERT(source_data.data() && source_data.size() == size_t(source_dimensions.x * source_dimensions.y * 4));
 
 	GLuint texture_id = 0;
 	glGenTextures(1, &texture_id);

Backends/RmlUi_Renderer_SDL.cpp

@@ -205,7 +205,7 @@ Rml::TextureHandle RenderInterface_SDL::LoadTexture(Rml::Vector2i& texture_dimen
 
 Rml::TextureHandle RenderInterface_SDL::GenerateTexture(Rml::Span<const Rml::byte> source, Rml::Vector2i source_dimensions)
 {
-	RMLUI_ASSERT(source.data() && source.size() == source_dimensions.x * source_dimensions.y * 4);
+	RMLUI_ASSERT(source.data() && source.size() == size_t(source_dimensions.x * source_dimensions.y * 4));
 
 #if SDL_MAJOR_VERSION >= 3
 	auto CreateSurface = [&]() {

Backends/RmlUi_Renderer_VK.cpp

@@ -485,7 +485,7 @@ Rml::TextureHandle RenderInterface_VK::LoadTexture(Rml::Vector2i& texture_dimens
 
 Rml::TextureHandle RenderInterface_VK::GenerateTexture(Rml::Span<const Rml::byte> source_data, Rml::Vector2i source_dimensions)
 {
-	RMLUI_ASSERT(source_data.data() && source_data.size() == source_dimensions.x * source_dimensions.y * 4);
+	RMLUI_ASSERT(source_data.data() && source_data.size() == size_t(source_dimensions.x * source_dimensions.y * 4));
 	Rml::String source_name = "generated-texture";
 	return CreateTexture(source_data, source_dimensions, source_name);
 }