fixes #194 Incorrect parse result when a variable precedes a skipped variable.

Author: harawata

src/main/java/org/apache/ibatis/parsing/GenericTokenParser.java

@@ -39,7 +39,7 @@ public String parse(String text) {
       while (start > -1) {
         if (start > 0 && src[start - 1] == '\\') {
           // the variable is escaped. remove the backslash.
-          builder.append(src, offset, start - 1).append(openToken);
+          builder.append(src, offset, start - offset - 1).append(openToken);
           offset = start + openToken.length();
         } else {
           int end = text.indexOf(closeToken, start);

src/test/java/org/apache/ibatis/parsing/GenericTokenParserTest.java

@@ -73,6 +73,8 @@ public void shallNotInterpolateSkippedVaiables() {
 
     assertEquals("${skipped} variable", parser.parse("\\${skipped} variable"));
     assertEquals("This is a ${skipped} variable", parser.parse("This is a \\${skipped} variable"));
+    assertEquals("null ${skipped} variable", parser.parse("${skipped} \\${skipped} variable"));
+    assertEquals("The null is ${skipped} variable", parser.parse("The ${skipped} is \\${skipped} variable"));
   }
 
   @Test(timeout = 1000)