Prevent php error when data was removed from redis (#149)

This code was already in redis storage but not in redisNg

Co-authored-by: Lukas Kämmerling <[email protected]>

Author: pluk77

src/Prometheus/Storage/RedisNg.php

@@ -415,6 +415,9 @@ private function collectHistograms(): array
         $histograms = [];
         foreach ($keys as $key) {
             $raw = $this->redis->hGetAll(str_replace($this->redis->_prefix(''), '', $key));
+            if (!isset($raw['__meta'])) {
+                continue;
+            }
             $histogram = json_decode($raw['__meta'], true);
             unset($raw['__meta']);
             $histogram['samples'] = [];
@@ -595,6 +598,9 @@ private function collectGauges(bool $sortMetrics = true): array
         $gauges = [];
         foreach ($keys as $key) {
             $raw = $this->redis->hGetAll(str_replace($this->redis->_prefix(''), '', $key));
+            if (!isset($raw['__meta'])) {
+                continue;
+            }
             $gauge = json_decode($raw['__meta'], true);
             unset($raw['__meta']);
             $gauge['samples'] = [];
@@ -632,6 +638,9 @@ private function collectCounters(bool $sortMetrics = true): array
         $counters = [];
         foreach ($keys as $key) {
             $raw = $this->redis->hGetAll(str_replace($this->redis->_prefix(''), '', $key));
+            if (!isset($raw['__meta'])) {
+                continue;
+            }
             $counter = json_decode($raw['__meta'], true);
             unset($raw['__meta']);
             $counter['samples'] = [];