Catch invalid input type to OpConvertUToPtr (#2078)

Fixes https://crbug.com/906426

* Fails validation if the input operand is a type
* Added a test

source/val/validate_conversion.cpp

@@ -248,7 +248,7 @@ spv_result_t ConversionPass(ValidationState_t& _, const Instruction* inst) {
                << spvOpcodeString(opcode);
 
       const uint32_t input_type = _.GetOperandTypeId(inst, 2);
-      if (!_.IsIntScalarType(input_type))
+      if (!input_type || !_.IsIntScalarType(input_type))
         return _.diag(SPV_ERROR_INVALID_DATA, inst)
                << "Expected int scalar as input: " << spvOpcodeString(opcode);
       break;

test/val/val_conversion_test.cpp

@@ -1279,6 +1279,29 @@ TEST_F(ValidateConversion, BitcastDifferentTotalBitWidth) {
           "Bitcast"));
 }
 
+TEST_F(ValidateConversion, ConvertUToPtrInputIsAType) {
+  const std::string spirv = R"(
+OpCapability Addresses
+OpCapability Shader
+OpCapability Linkage
+OpMemoryModel Logical GLSL450
+%int = OpTypeInt 32 0
+%ptr_int = OpTypePointer Function %int
+%void = OpTypeVoid
+%voidfn = OpTypeFunction %void
+%func = OpFunction %void None %voidfn
+%entry = OpLabel
+%1 = OpConvertUToPtr %ptr_int %int
+OpReturn
+OpFunctionEnd
+)";
+
+  CompileSuccessfully(spirv);
+  EXPECT_EQ(SPV_ERROR_INVALID_DATA, ValidateInstructions());
+  EXPECT_THAT(getDiagnosticString(),
+              HasSubstr("Expected int scalar as input: ConvertUToPtr"));
+}
+
 }  // namespace
 }  // namespace val
 }  // namespace spvtools