MYST3: Clear the screen with solid black

Fixes unintentional transparency when loading games from the menu

engines/myst3/gfx_opengl.cpp

@@ -83,6 +83,7 @@ void OpenGLRenderer::init() {
 }
 
 void OpenGLRenderer::clear() {
+	glClearColor(0.f, 0.f, 0.f, 1.f); // Solid black
 	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 	glColor3f(1.0f, 1.0f, 1.0f);
 }

engines/myst3/gfx_opengl_shaders.cpp

@@ -163,6 +163,7 @@ void ShaderRenderer::init() {
 }
 
 void ShaderRenderer::clear() {
+	glClearColor(0.f, 0.f, 0.f, 1.f); // Solid black
 	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 }