don't fail when the root node doesn't have a source section

Author: timfel

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/code/CodeBuiltins.java

@@ -103,7 +103,12 @@ public abstract static class LinenoNode extends PythonBuiltinNode {
         @TruffleBoundary
         protected Object doIt(PythonParseResult self) {
             RootNode rootNode = self.getRootNode();
-            return rootNode.getSourceSection().getStartLine();
+            SourceSection sourceSection = rootNode.getSourceSection();
+            if (sourceSection == null) {
+                return 1;
+            } else {
+                return sourceSection.getStartLine();
+            }
         }
     }