Bypass descryption in case that file's size is 0
Bypass descryption in case that file's size is 0

Until now, crosswalk-tizen does descryption although the files' contents
are empty(the file size is 0). It's ineffective.
Fix code to bypass it in the case.

psikorski/crosswalk-tizen,psikorski/crosswalk-tizen,psikorski/crosswalk-tizen,psikorski/crosswalk-tizen