do not apply rotation if the screen is not portrait screen

Author: joshuatam

src/Backends/DRMBackend.cpp

@@ -3031,10 +3031,12 @@ bool drm_set_mode( struct drm_t *drm, const drmModeModeInfo *mode )
 		g_nOutputWidth = mode->hdisplay;
 		g_nOutputHeight = mode->vdisplay;
 
-		if (g_bUseRotationShader) {
+		if (g_bUseRotationShader && mode->vdisplay > mode->hdisplay) {
 			g_bRotated = true;
 			g_nOutputWidth = mode->vdisplay;
 			g_nOutputHeight = mode->hdisplay;
+		} else {
+			g_bUseRotationShader = false;
 		}
 
 		break;