Fixed possible endless loop in Boo ExpressionFinder.

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/trunk@612 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/AddIns/BackendBindings/Boo/BooBinding/Project/Src/CodeCompletion/ExpressionFinder.cs

@@ -265,6 +265,9 @@ namespace Grunwald.BooBinding.CodeCompletion
 						b.Append(inText, offset + 1, i - offset - 1);
 						result.Expression = b.ToString();
 						return result;
+					} else if (c == '\0') {
+						// end of document
+						break;
 					}
 				}
 				bracket = _closingBrackets.IndexOf(c);