Fixed a bug in two funnctions which caused zimdump to cause a segmentation fault when the url passed was not found in the zim file. The error occurred when the tool attempts to display the article.

Change-Id: Ica90f36dc7b8aef93de9581355030b6f08a2ca61
Bug Fix for bug no 52324 on openzim. Sorts the MIME Types before storing them to file.

Since this will be the new standard, the old ZIM files will have to be generated gain in order to obtain checksum match during zimdiff/zimpatch

Change-Id: I37a32d4d9adad7402ab7dbb0d9bee143b76d89b7
Merge commit 'refs/changes/21/79021/1' of https://gerrit.wikimedia.org/r/openzim
fix style