Fix issues with starting sponge

I got the following error block after installing 1.1.0 on every new tab.

```
contains: Key not specified
test: Unexpected argument type at index 1
= true -a true = true
 ^
~/.config/fish/functions/sponge_filter_failed.fish (line 4):
  if test $previously_in_history = true -a $sponge_allow_previously_successful = true
     ^
in function 'sponge_filter_failed' with arguments '0 ""'
	called on line 14 of file ~/.config/fish/functions/_sponge_on_postexec.fish
in function '_sponge_on_postexec'
	called on line 1 of file ~/.config/fish/config.fish
in event handler: handler for generic event “fish_postexec”
	called on line 378 of file ~/.config/fish/config.fish
```

This fixes both issues. Everything else *appears* to work. This may
address meaningful-ooo#4.

functions/_sponge_on_postexec.fish

@@ -1,24 +1,30 @@
 function _sponge_on_postexec --on-event fish_postexec
+  # Ignore empty commands
+  if test -n $_sponge_current_command
+    return
+  end
+
   set --global _sponge_current_command_exit_code $status
 
   # Remove command from the queue if it's been added previously
   if set --local index (contains --index -- $_sponge_current_command $_sponge_queue)
     set --erase _sponge_queue[$index]
   end
 
-  # Ignore empty commands
-  if test -n $_sponge_current_command
-    set --local command ''
-    # Run filters
-    for filter in $sponge_filters
-      if $filter \
-          $_sponge_current_command \
-          $_sponge_current_command_exit_code \
-          $_sponge_current_command_previously_in_history
-        set command $_sponge_current_command
-        break
-      end
+  if ! test -n "$_sponge_current_command_previously_in_history"
+    set _sponge_current_command_previously_in_history false
+  end
+
+  set --local command ''
+  # Run filters
+  for filter in $sponge_filters
+    if $filter \
+        $_sponge_current_command \
+        $_sponge_current_command_exit_code \
+        "$_sponge_current_command_previously_in_history"
+      set command $_sponge_current_command
+      break
     end
-    set --prepend --global _sponge_queue $command
   end
+  set --prepend --global _sponge_queue $command
 end

functions/sponge_filter_failed.fish

@@ -1,11 +1,11 @@
 function sponge_filter_failed \
   --argument-names command exit_code previously_in_history
 
-  if test $previously_in_history = true -a $sponge_allow_previously_successful = true
+  if test "$previously_in_history" = true -a "$sponge_allow_previously_successful" = true
     return 1
   end
 
-  if contains $exit_code $sponge_successful_exit_codes
+  if contains -- $exit_code $sponge_successful_exit_codes
     return 1
   end
 end