#369 Check return codes everywhere

[Markus Elfring]

Some checks for return codes are missing.

Examples:
Would you like to add more error handling for return values from "WaitForSingleObject" like in the constructor "MutexLock" and from "CreateSolidBrush" in the member function "ImageHandler::CreateRelativeImage"?
http://console.git.sourceforge.net/git/gitweb.cgi?p=console/console;a=blob;f=Console/Helpers.h;h=d611e511bda2259ed5078e5351d1aea758224272;hb=HEAD
http://console.git.sourceforge.net/git/gitweb.cgi?p=console/console;a=blob;f=Console/ImageHandler.cpp;h=986aa38225d2bc297fef0467bef4ad8b0438e5f2;hb=HEAD