[FIX] mail: replace special characters

When the delimiter '@' is used in the composer, a regular expression is
built in order to suggest followers. However, if this regular expression
is incorrect, it causes a crash since RegExp will throw a syntax error.
Since a new regular expression is built for each new character the user
types, this situation can occur very easily. For example, typing '@('
will cause a crash.

This fix replaces characters which may easily lead to a syntax error by
a space.

addons/mail/static/src/js/composer.js

@@ -23,6 +23,7 @@ var accented_letters_mapping = {
     'oe': 'œ',
     'u': '[ùúûűü]',
     'y': '[ýÿ]',
+    ' ': '[()\\[\\]]',
 };
 
 // The MentionManager allows the Composer to register listeners. For each