Fix bspatch heap overflow vulnerability.

Obtained from:	Chromium
Reported by:	Lu Tung-Pin
Security:	FreeBSD-SA-16:25.bspatch

usr.bin/bsdiff/bspatch/bspatch.c

@@ -163,6 +163,10 @@ int main(int argc,char * argv[])
 			ctrl[i]=offtin(buf);
 		}
 
+		/* Sanity-check */
+		if ((ctrl[0] < 0) || (ctrl[1] < 0))
+			errx(1,"Corrupt patch\n");
+
 		/* Sanity-check */
 		if(newpos+ctrl[0]>newsize)
 			errx(1,"Corrupt patch\n");