mailsplit: fix for more than one input files

Earlier commit d63bd9a broke the case where more than one input
files are fed to mailsplit by not incrementing the base counter
when splitting second and subsequent input files.  This should
fix it.

Signed-off-by: Junio C Hamano <junkio@cox.net>

builtin-mailsplit.c

@@ -261,7 +261,8 @@ int cmd_mailsplit(int argc, const char **argv, const char *prefix)
 				error("cannot split patches from stdin");
 				return 1;
 			}
-			num += ret;
+			num += (ret - nr);
+			nr = ret;
 			continue;
 		}
 
@@ -279,7 +280,8 @@ int cmd_mailsplit(int argc, const char **argv, const char *prefix)
 			error("cannot split patches from %s", arg);
 			return 1;
 		}
-		num += ret;
+		num += (ret - nr);
+		nr = ret;
 	}
 
 	printf("%d\n", num);