fix(tsdb): Fix panic, don't add nil iterator to slice

fixes #10171

tsdb/index.go

@@ -2179,10 +2179,11 @@ func (is IndexSet) matchTagValueEqualEmptySeriesIDIterator(name, key []byte, val
 				itr, err := is.tagValueSeriesIDIterator(name, key, e)
 				if err != nil {
 					return err
-				}
+				} else if itr != nil {
 					itrs = append(itrs, itr)
 				}
 			}
+		}
 		return nil
 	}(); err != nil {
 		SeriesIDIterators(itrs).Close()
@@ -2222,10 +2223,11 @@ func (is IndexSet) matchTagValueEqualNotEmptySeriesIDIterator(name, key []byte,
 			if err != nil {
 				SeriesIDIterators(itrs).Close()
 				return nil, err
-			}
+			} else if itr != nil {
 				itrs = append(itrs, itr)
 			}
 		}
+	}
 	return MergeSeriesIDIterators(itrs...), nil
 }
 
@@ -2253,10 +2255,11 @@ func (is IndexSet) matchTagValueNotEqualEmptySeriesIDIterator(name, key []byte,
 			if err != nil {
 				SeriesIDIterators(itrs).Close()
 				return nil, err
-			}
+			} else if itr != nil {
 				itrs = append(itrs, itr)
 			}
 		}
+	}
 	return MergeSeriesIDIterators(itrs...), nil
 }
 
@@ -2283,10 +2286,11 @@ func (is IndexSet) matchTagValueNotEqualNotEmptySeriesIDIterator(name, key []byt
 			if err != nil {
 				SeriesIDIterators(itrs).Close()
 				return nil, err
-			}
+			} else if itr != nil {
 				itrs = append(itrs, itr)
 			}
 		}
+	}
 
 	mitr, err := is.measurementSeriesIDIterator(name)
 	if err != nil {