Fix heap overflow in `iniparser_dumpsection_ini()`

...reported in #177

As suggested by the issue reporter this is fixed by returning from
`iniparser_dumpsection_ini()` in case the length of the passed section name
of dictionary to dump was bigger than the size of the internal buffer used
to copy this string to.

Changelog: changed

src/iniparser.c

@@ -327,6 +327,7 @@ void iniparser_dumpsection_ini(const dictionary * d, const char * s, FILE * f)
 
     if (d==NULL || f==NULL) return;
     if (! iniparser_find_entry(d, s)) return;
+    if (strlen(s) > sizeof(keym)) return;
 
     seclen  = (int)strlen(s);
     fprintf(f, "\n[%s]\n", s);