opengl: Set the color to full alpha in the non-shader draw path

The color is set when drawing subpictures, but wasn't set when
drawing the main texture.

For some reason, the current color was reset between each
display call in some environments, making this issue not to be
visible.
Signed-off-by: Martin Storsjö <martin@martin.st>

modules/video_output/opengl.c

@@ -851,6 +851,7 @@ static void DrawWithoutShaders(vout_display_opengl_t *vgl,
         right[0], top[0]
     };
 
+    glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
     glEnable(vgl->tex_target);
     glActiveTexture(GL_TEXTURE0 + 0);
     glClientActiveTexture(GL_TEXTURE0 + 0);