BBitmap: Amend special-casing for B_RGB32 in SetBits.

* Spirograph uses SetBits with length 1 und 4, which can't work as
expected. As Spirograph uses the same source and target colorspace,
the memcpy codepath is used with the right length.
* fix #12931

Change-Id: I4f27e748fb842c2d81d4161e7c94586844995bdf
Reviewed-on: https://review.haiku-os.org/c/haiku/+/8562
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: Adrien Destugues <[email protected]>
Haiku-Format: Haiku-format Bot <[email protected]>

src/kits/interface/Bitmap.cpp

@@ -665,8 +665,8 @@ BBitmap::SetBits(const void* data, int32 length, int32 offset,
 	int32 inBPR = -1;
 	// tweaks to mimic R5 behavior
 	if (error == B_OK) {
-		if (colorSpace == B_RGB32) {
-			// B_RGB32 means actually unpadded B_RGB24_BIG
+		if (colorSpace == B_RGB32 && (length % 3) == 0) {
+			// B_RGB32 could actually mean unpadded B_RGB24_BIG
 			colorSpace = B_RGB24_BIG;
 			inBPR = width * 3;
 		} else if (colorSpace == B_CMAP8 && fColorSpace != B_CMAP8) {