lib/gcd.c: prevent possible div by 0

Account for all properties when a and/or b are 0:
gcd(0, 0) = 0
gcd(a, 0) = a
gcd(0, b) = b

Fixes no known problems in current kernels.
Signed-off-by: Davidlohr Bueso <dave@gnu.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/gcd.c

@@ -9,6 +9,9 @@ unsigned long gcd(unsigned long a, unsigned long b)
 
 	if (a < b)
 		swap(a, b);
+
+	if (!b)
+		return a;
 	while ((r = a % b) != 0) {
 		a = b;
 		b = r;