Found by gcc-7.1 which reported build error as:

rts/ProfilerReportJson.c:23:16: error:
     error: comparison between pointer and zero
       character constant [-Werror=pointer-compare]
         for (; str != '\0' && len > 0; str++) {
                    ^~
   |
23 |     for (; str != '\0' && len > 0; str++) {
   |                ^

Unfixed code in context:

```c
  static void escapeString(char const* str, char *out, int len)
  {
     len--; // reserve character in output for terminating NUL
     for (; str != '\0' && len > 0; str++) {
         char c = *str;
```

The intent here is to process 'len' (if positive) or '\0'-terminator
in 'str' but dereference was missing.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>