Fixed unhandled LTL parse error exception

src/main/java/de/tlc4b/TLC4B.java

src/main/java/de/tlc4b/ltl/LTLFormulaVisitor.java

src/test/java/de/tlc4b/tlc/integration/BasicTest.java

src/test/java/de/tlc4b/tlc/integration/BugTest.java

src/test/resources/bugs/LTLParseError.mch