wordexp p is now initialized to {0} to prevent a segfault on wordfree
in the failure case.
File paths with single quotes and double quotes are now supported. The
quote can either be wrapped in the other quote or escaped with three
backslashes.
Additionally to make passing file paths with double quotes to swaybg
easier, instead of enclosing the path given to swaybg in quotes, all
spaces, single quotes, and double quotes in the resulting path are now
escaped with a single backslash.
This allows for a color to be set when the wallpaper does not fill the
entire output. If specified, the fallback color is also used when the
image path is inaccessible.
- fixes a double-free error when access() failed.
- refactor code to make memory managment (alloc/free) more straightforward
- do not bring the temporary wordexp_t struct around
- do not postpone errors handling
if src is NULL due to a previous error we cannot use it in the command
result string.
Moreover if `src` points to `p.we_wordv[0]` we cannot use it after
`wordfree(&p)` in the command result string.
Bonus feature: If there was an error accessing the file, the string
rapresentation of the error is now included in the command result
string.
