simoop: make sure oddsizes never returns zero sizes

Signed-off-by: Chris Mason <clm@fb.com>

simoop.c

diff --git a/simoop.c b/simoop.c
index fac500a..f73bb64 100644
--- a/simoop.c
+++ b/simoop.c
@@ -1010,10 +1010,15 @@
 
 static loff_t randomize_size(loff_t sz)
 {
+	loff_t val;
 	if (!oddsizes)
 		return sz;
 
-	return rand() % sz;
+	val = rand() % sz;
+	if (val == 0)
+		val = sz;
+
+	return val;
 }
 
 static void maybe_fsync(int fd)