bugfix: get tests to pass

Manual_tests.md

@@ -13,6 +13,8 @@ record those here.
   graphics printed to screen, but not the precise pixels they translate to.
     - where exactly the cursor is drawn to highlight a given character
 
+* Logging files created in the 'recent' file.
+
 ### Other compromises
 
 Lua is dynamically typed. Tests can't patch over lack of type-checking.

file.lua

@@ -49,10 +49,12 @@ function save_to_disk(State)
   end
   outfile:close()
   if not State.recent_updated then
-    local f = io.open(State.directory..'recent', 'a')
-    if f then
-      f:write(State.file_path, '\n')
-      f:close()
+    if State.file_path then  -- might not be set in some tests from lines.love that I don't want to modify in capture.love; we don't want to touch the file system then anyway
+      local f = io.open(State.directory..'recent', 'a')
+      if f then
+        f:write(State.file_path, '\n')
+        f:close()
+      end
     end
     State.recent_updated = true
   end