Fix use of uninitialized variable 's' (reported by Coverity)

If the MAXREPEATS constant is set to be small, then the variable
's' could be left uninitialized and then used in computations.

main.c

@@ -90,7 +90,7 @@ static double bandwidth_bench_helper(int64_t *dstbuf, int64_t *srcbuf,
     double s, s0, s1, s2;
 
     /* do up to MAXREPEATS measurements */
-    s0 = s1 = s2 = 0;
+    s = s0 = s1 = s2 = 0;
     maxspeed   = 0;
     for (n = 0; n < MAXREPEATS; n++)
     {
@@ -139,7 +139,7 @@ static double bandwidth_bench_helper(int64_t *dstbuf, int64_t *srcbuf,
         }
     }
 
-    if (s / maxspeed * 100. >= 0.1)
+    if (maxspeed > 0 && s / maxspeed * 100. >= 0.1)
     {
         printf("%s%-52s : %8.1f MB/s (%.1f%%)\n", indent_prefix, description,
                                                maxspeed, s / maxspeed * 100.);