[Feature request] Turn missing font segfault into a fatal error with a friendly message

So, this is Day 1 with 4coder for me, having a lot of fun hacking around with it :)

after building my custom_4coder.so I bundled it with the other binaries and put them in a bin/ directory in my project directory. ( I was thinking that it would be best just to have a copy of 4coder with every project, because I was thinking I might want a different custom_4coder.so for each projects and bundling the other binaries with it ensures that they will all work together, (I'm not sure if there are linking incompatibilities between versions). This pattern might be a mistake, who knows its the first thing I tried...

Anyway, I forgot the font directory, and so I hit this:

Thread 1 "4ed" received signal SIGSEGV, Segmentation fault.
0x00007ffff3f24132 in font_get_or_make_page (system=0x619140 <linuxvars+13856>, 
    system@entry=0x7fffd38d2048, font=0x0, font@entry=0x622720, page_number=page_number@entry=0)
    at /home/allen/Documents/4coder/code/4ed_font_static_functions.cpp:193

For me it was pretty easy to figure out what was going on, but other people might not. So I was going to recommend that there be a nice user friendly message to the user why it is crashing... kinda like the messages about missing ".so" files you already have. (Which is a really nice touch by the way :) )

Anyway, this isn't really very important but thought I might mention it...

Linux Ubuntu 16.04.2 LTS 4.0.20 Super