Fix empty do-while loop parsing (close #133)

slither/solc_parsing/declarations/function.py

@@ -313,7 +313,11 @@ class FunctionSolc(Function):
         node_endDoWhile = self._new_node(NodeType.ENDLOOP, doWhilestatement['src'])
 
         link_nodes(node, node_startDoWhile)
-        link_nodes(node_startDoWhile, node_condition.sons[0])
+        # empty block, loop from the start to the condition
+        if not node_condition.sons:
+            link_nodes(node_startDoWhile, node_condition)
+        else:
+            link_nodes(node_startDoWhile, node_condition.sons[0])
         link_nodes(statement, node_condition)
         link_nodes(node_condition, node_endDoWhile)
         return node_endDoWhile