OverlayWndProc: Fix flickering issue

The flickering was caused by DefWindowProc trying to erase the background, then GDI painting back in the bitmap. By not letting DefWindowProc draw the background, flickering is effectively removed.

git-svn-id: svn://vcs.sdm.2ki.xyz/Grabby/trunk@15 27729192-006e-004d-b9b5-06fbd0ef7001

Overlay.c

@@ -179,6 +179,9 @@ OverlayWndProc(HWND hWnd,
 
 		EndPaint(hWnd, &ps);
 		break;
+	case WM_ERASEBKGND:
+		// Do nothing
+		return 1;
 	case WM_MOUSEMOVE:
 		if (isDrag && (wParam & MK_LBUTTON)) {
 			POINTS ptPrev = ptCur;