Merge #3618

3618: Update missing file from #3600 update r=def- a=Jupeyy

It was probs added between the reverted updates redone in #3600 and the first tool update, so i missed it.

Also took the chance to make the tool safer, so this doesnt happen again

## Checklist

- [ ] Tested the change ingame
- [ ] Provided screenshots if it is a visual change
- [ ] Tested in combination with possibly related configuration options
- [ ] Written a unit test if it works standalone, system.c especially
- [ ] Considered possible null pointers and out of bounds array indexing
- [ ] Changed no physics that affect existing maps
- [ ] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional)


Co-authored-by: Jupeyy <jupjopjap@gmail.com>

src/engine/shared/image_manipulation.cpp

@@ -61,7 +61,10 @@ static void CopyColorValues(int w, int h, int BPP, unsigned char *pSrc, unsigned
 		for(int x = 0; x < w; x++, m += BPP)
 		{
 			for(int i = 0; i < BPP - 1; ++i)
-				pDest[m + i] = pSrc[m + i];
+			{
+				if(pDest[m + 3] == 0)
+					pDest[m + i] = pSrc[m + i];
+			}
 		}
 	}
 }