[crystal mode] Fix an infinite loop in tokenizing of heredoc strings

Closes #7092

Author: marijnh

mode/crystal/crystal.js

@@ -379,7 +379,7 @@
               return "string";
             }
 
-            escaped = embed && stream.next() == "\\";
+            escaped = stream.next() == "\\" && embed;
           } else {
             stream.next();
             escaped = false;