Fix syntax error return in parenthesised term

part of #9

src/main/java/edu/kit/typicalc/model/parser/LambdaParser.java

@@ -224,6 +224,9 @@ public class LambdaParser {
                     return new Result<>(null, error.get().expectedInput(ExpectedInput.TERM));
                 }
                 Result<LambdaTerm, ParseError> term = parseTerm(false);
+                if (term.isError()) {
+                    return term; // return error early
+                }
                 error = expect(TokenType.RIGHT_PARENTHESIS);
                 if (error.isEmpty()) {
                     return term;

src/test/java/edu/kit/typicalc/model/parser/LambdaParserTest.java

@@ -7,6 +7,7 @@ import nl.jqno.equalsverifier.EqualsVerifier;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 class LambdaParserTest {
     private static final VarTerm X = new VarTerm("x");
@@ -202,6 +203,15 @@ class LambdaParserTest {
         assertEquals(3, error.getPosition());
     }
 
+    @Test
+    void errorCase1() {
+        LambdaParser parser = new LambdaParser("(λx.x)(λ");
+        ParseError error = parser.parse().unwrapError();
+        assertEquals(TokenType.EOF, error.getCause().get().getType());
+        assertEquals(1, error.getExpected().get().size());
+        assertTrue(error.getExpected().get().contains(TokenType.VARIABLE));
+    }
+
     @Test
     void equality() {
         EqualsVerifier.forClass(Token.class).usingGetClass().verify();