Fix omitted return post failed parse

PiperOrigin-RevId: 228903905

mlir/lib/Parser/Parser.cpp

@@ -1102,6 +1102,8 @@ Attribute Parser::parseAttribute(Type type) {
       auto valuesEltType = type.getElementType();
       auto values =
           parseDenseElementsAttr(valuesEltType, type.isa<VectorType>());
+      if (!values)
+        return nullptr;
 
       /// Sanity check.
       auto indicesType = indices.getType();

mlir/test/IR/invalid.mlir

@@ -851,3 +851,9 @@ func @complex_loops() {
   for %i1 = 1 to 100 {
   // expected-error @+1 {{expected '"' in string literal}}
   "opaqueIntTensor"(){bar: opaque<tensor<2x1x4xi32>, "0x686]>} : () -> ()
+
+// -----
+
+func @mi() {
+  // expected-error @+1 {{expected '[' or scalar constant inside tensor literal}}
+  "fooi64"(){bar: sparse<vector<1xi64>,[,[,1]