fix(int): Simplify test and make static analysis happy

The prior test was redundant. Since a few lines above, if B was an
image but A was not, we swapped to ensure that A was always an
image. So here, we can just test A to know for sure that at least one
of them is an image. That makes the test here simpler, but it also
makes it more clear to static analysis that from this point forward, A
can't be nullptr.

Signed-off-by: Larry Gritz <[email protected]>

src/libOpenImageIO/imagebufalgo_mad.cpp

@@ -147,7 +147,7 @@ ImageBufAlgo::mad(ImageBuf& dst, Image_or_Const A_, Image_or_Const B_,
         A_.swap(B_);
     // Get pointers to any image. At least one of A or B must be an image.
     const ImageBuf *A = A_.imgptr(), *B = B_.imgptr(), *C = C_.imgptr();
-    if (!A && !B) {
+    if (!A) {
         dst.errorfmt(
             "ImageBufAlgo::mad(): at least one of the first two arguments must be an image");
         return false;