Fix source section off-by-one error, fix source sections for leaf nodes

Author: numberpi

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/parser/PythonBaseTreeTranslator.java

@@ -162,7 +162,7 @@ public Object visitChildren(RuleNode node) {
     }
 
     protected void deriveSourceSection(RuleNode node, Object r) {
-        if (r instanceof PNode) {
+        if (r instanceof PNode && ((PNode) r).getSourceSection() == null) {
             SourceSection derivedSection = deriveSourceSection(node);
             if (derivedSection != null) {
                 ((PNode) r).assignSourceSection(derivedSection);
@@ -186,7 +186,7 @@ private SourceSection deriveSourceSection(RuleNode node) {
         } else if (node instanceof ParserRuleContext) {
             int start = ((ParserRuleContext) node).getStart().getStartIndex();
             int stop = ((ParserRuleContext) node).getStop().getStopIndex();
-            return createSourceSection(start, stop - start);
+            return createSourceSection(start, stop - start + 1);
         }
         return null;
     }