Correctly handle the case that a parenthesis is empty.

Resolves #1178

Author: gunterkoenigsmann

src/ParenCell.cpp

@@ -389,6 +389,9 @@ void ParenCell::Draw(wxPoint point)
 wxString ParenCell::ToString()
 {
   wxString s;
+  if(!m_innerCell)
+    return "()";
+  
   if (!m_isBrokenIntoLines)
   {
     if (m_print)

src/main.cpp

@@ -194,7 +194,7 @@ bool MyApp::OnInit()
   {
     std::cout << "A feature-rich graphical user interface for the computer algebra system maxima\n";
     std::cout << cmdLineParser.GetUsageString();
-    exit(wxMaxima::m_exitCode);
+    exit(0);
   }
 
   if(cmdLineError != 0)