Gracefully fail when history file is inaccessible (#2410)

If the history file (or its parents) can't be created, running a command
will fail entirely. Since saving command history is not an integral part
of running a command, it would be nicer if it carried on, just without
saving history. This is what shells usually do.

This patch removes assertions in the history saving function and
instead adds an early return, so if the history isn't saved the command
invocation simply carries on.

Signed-off-by: Alyssa Ross <hi@alyssa.is>

lib/awful/prompt.lua

@@ -110,7 +110,6 @@
 -- @see string
 
 -- Grab environment we need
-local assert = assert
 local io = io
 local table = table
 local math = math
@@ -210,8 +209,12 @@ end
 -- @param id The data.history identifier
 local function history_save(id)
     if data.history[id] then
-        assert(gfs.make_parent_directories(id))
-        local f = assert(io.open(id, "w"))
+        gfs.make_parent_directories(id)
+        local f = io.open(id, "w")
+        if not f then
+            gdebug.print_warning("Failed to write the history to "..id)
+            return
+        end
         for i = 1, math.min(#data.history[id].table, data.history[id].max) do
             f:write(data.history[id].table[i] .. "\n")
         end