Improve the DynamicMeter_search API to make 'key' optional

Thanks to @BenBE for the suggestion.

DynamicMeter.c

@@ -52,7 +52,8 @@ bool DynamicMeter_search(Hashtable* dynamics, const char* name, unsigned int* ke
    DynamicIterator iter = { .key = 0, .name = name, .found = false };
    if (dynamics)
       Hashtable_foreach(dynamics, DynamicMeter_compare, &iter);
-   *key = iter.key;
+   if (key)
+      *key = iter.key;
    return iter.found;
 }
 

pcp/PCPDynamicMeter.c

@@ -140,8 +140,7 @@ static bool PCPDynamicMeter_validateMeterName(char* key, const char* path, unsig
 
 // Ensure a meter name has not been defined previously
 static bool PCPDynamicMeter_uniqueName(char* key, const char* path, unsigned int line, PCPDynamicMeters* meters) {
-   unsigned int param = 0;
-   if (DynamicMeter_search(meters->table, key, &param) == false)
+   if (DynamicMeter_search(meters->table, key, NULL) == false)
       return true;
 
    fprintf(stderr, "%s: duplicate name at %s line %u: \"%s\", ignored\n",
@@ -199,6 +198,7 @@ static void PCPDynamicMeter_parseFile(PCPDynamicMeters* meters, const char* path
          if (caption) {
             free_and_xStrdup(&meter->super.caption, caption);
             free(caption);
+	    caption = NULL;
          }
       } else if (value && meter && String_eq(key, "description")) {
          free_and_xStrdup(&meter->super.description, value);