GL: Disabled scissor test when using clear quad.

src/renderer_gl.cpp

@@ -2218,6 +2218,7 @@ namespace bgfx
 #if BGFX_CONFIG_CLEAR_QUAD
 		if (s_renderCtx.m_useClearQuad)
 		{
+			GL_CHECK(glDisable(GL_SCISSOR_TEST) );
 			GL_CHECK(glDisable(GL_CULL_FACE) );
 			GL_CHECK(glDisable(GL_BLEND) );