Fix wrong mutex stats in json-formatted malloc stats

During mutex stats emit, derived counters are not emitted for json.
Yet the array indexing counter should still be increased to skip
derived elements in the output, which was not. This commit fixes it.

src/stats.c

@@ -260,10 +260,10 @@ mutex_stats_emit(emitter_t *emitter, emitter_row_t *row,
 #define OP(counter, type, human, derived, base_counter)                        \
 	if (!derived) {                                                        \
 		col = &col_##type[k_##type];                                   \
-		++k_##type;                                                    \
 		emitter_json_kv(emitter, #counter, EMITTER_TYPE_##type,        \
 		    (const void *)&col->bool_val);                             \
-	}
+	}                                                                      \
+	++k_##type;
 	MUTEX_PROF_COUNTERS;
 #undef OP
 #undef EMITTER_TYPE_uint32_t