feh v2.18.3

Fix double-free/OOB-write in E17 IPC. This only affects the background setting options and requires a malicious X11 app to run alongside feh and pretend to be an E17 window manager. (patch by Tobias Stoeckmann)
Fix image-specific format specifiers not being updated correctly in thumbnail mode window titles
Fix memory leak when closing images opened from thumbnail mode
Fix a possible out of bounds read caused by an unterminated string when using --output to save images in long paths. (patch by Tobias Stoeckmann)
Fix out of bounds read/write when handling empty or broken caption files. (patch by Tobias Stoeckmann)
Fix memory leak when saving a filelist or image whose target filename already exists. (patch by Tobias Stoeckmann)