chore: Fix panic for queries with unsupported predicate types (backport k270) (#19087)

Co-authored-by: benclive <[email protected]>

Author: loki-gh-app[bot]

pkg/dataobj/metastore/object.go

@@ -416,6 +416,10 @@ func pointerPredicateFromMatchers(matchers ...*labels.Matcher) pointers.RowPredi
 		}
 	}
 
+	if len(predicates) == 0 {
+		return nil
+	}
+
 	current := predicates[0]
 
 	for _, predicate := range predicates[1:] {

pkg/dataobj/metastore/object_test.go

@@ -335,6 +335,16 @@ func TestSectionsForStreamMatchers(t *testing.T) {
 			predicates: nil,
 			wantCount:  0,
 		},
+		{
+			name: "matching selector with unsupported predicate type",
+			matchers: []*labels.Matcher{
+				labels.MustNewMatcher(labels.MatchEqual, "app", "foo"),
+			},
+			predicates: []*labels.Matcher{
+				labels.MustNewMatcher(labels.MatchRegexp, "bar", "something"),
+			},
+			wantCount: 1,
+		},
 	}
 
 	for _, tt := range tests {