Reset exception state when initializing context.

Author: fangerer

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/nodes/control/TopLevelExceptionHandler.java

@@ -117,8 +117,6 @@ public Object execute(VirtualFrame frame) {
                     }
                 }
                 throw e;
-            } finally {
-                context.setCurrentException(null);
             }
         }
     }

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/runtime/PythonContext.java

@@ -191,6 +191,7 @@ public void initialize() {
         mainModule = core.factory().createPythonModule(__MAIN__);
         mainModule.setAttribute(__BUILTINS__, builtinsModule);
         sysModules.setItem(__MAIN__, mainModule);
+        currentException = null;
 
         isInitialized = true;
     }