Fix test issues from introduction of HRANDFIELD (#8424)

* The corrupt dump fuzzer found a division by zero.
* in some cases the random fields from the HRANDFIELD tests produced
  fields with newlines and other special chars (due to \ char), this caused
  the TCL tests to see a bulk response that has a newline in it and add {}
  around it, later it can think this is a nested list. in fact the `alpha` random
  string generator isn't using spaces and newlines, so it should not use `\`
  either.

src/ziplist.c

@@ -1506,6 +1506,9 @@ void ziplistRandomPair(unsigned char *zl, unsigned long total_count, ziplistEntr
     int ret;
     unsigned char *p;
 
+    /* Avoid div by zero on corrupt ziplist */
+    assert(total_count);
+
     /* Generate even numbers, because ziplist saved K-V pair */
     int r = (rand() % total_count) * 2;
     p = ziplistIndex(zl, r);
@@ -1545,6 +1548,9 @@ void ziplistRandomPairs(unsigned char *zl, int count, ziplistEntry *keys, ziplis
     rand_pick *picks = zmalloc(sizeof(rand_pick)*count);
     unsigned long total_size = ziplistLen(zl)/2;
 
+    /* Avoid div by zero on corrupt ziplist */
+    assert(total_size);
+
     /* create a pool of random indexes (some may be duplicate). */
     for (int i = 0; i < count; i++) {
         picks[i].index = (rand() % total_size) * 2; /* Generate even indexes */

tests/integration/corrupt-dump.tcl

@@ -507,5 +507,16 @@ test {corrupt payload: fuzzer findings - valgrind invalid read} {
     }
 }
 
+test {corrupt payload: fuzzer findings - HRANDFIELD on bad ziplist} {
+    start_server [list overrides [list loglevel verbose use-exit-on-panic yes crash-memcheck-enabled no] ] {
+        r config set sanitize-dump-payload yes
+        r debug set-skip-checksum-validation 1
+        r RESTORE _int 0 "\x04\xC0\x01\x09\x00\xF6\x8A\xB6\x7A\x85\x87\x72\x4D"
+        catch {r HRANDFIELD _int}
+        assert_equal [count_log_message 0 "crashed by signal"] 0
+        assert_equal [count_log_message 0 "ASSERTION FAILED"] 1
+    }
+}
+
 } ;# tags
 

tests/support/util.tcl

@@ -12,7 +12,11 @@ proc randstring {min max {type binary}} {
         set maxval 52
     }
     while {$len} {
-        append output [format "%c" [expr {$minval+int(rand()*($maxval-$minval+1))}]]
+        set rr [expr {$minval+int(rand()*($maxval-$minval+1))}]
+        if {$type eq {alpha} && $rr eq 92} {
+            set rr 90; # avoid putting '\' char in the string, it can mess up TCL processing
+        }
+        append output [format "%c" $rr]
         incr len -1
     }
     return $output