Fix enabling buffer when plugin disabled

Fixes #803.

autoload/gitgutter.vim

@@ -21,6 +21,10 @@ endfunction
 function! gitgutter#process_buffer(bufnr, force) abort
   " NOTE a:bufnr is not necessarily the current buffer.
 
+  if gitgutter#utility#getbufvar(a:bufnr, 'enabled', -1) == -1
+    call gitgutter#utility#setbufvar(a:bufnr, 'enabled', g:gitgutter_enabled)
+  endif
+
   if gitgutter#utility#is_active(a:bufnr)
 
     if has('patch-7.4.1559')
@@ -55,12 +59,11 @@ endfunction
 
 
 function! gitgutter#disable() abort
-  " get list of all buffers (across all tabs)
   for bufnr in range(1, bufnr('$') + 1)
     if buflisted(bufnr)
       let file = expand('#'.bufnr.':p')
       if !empty(file)
-        call s:clear(bufnr)
+        call gitgutter#buffer_disable(bufnr)
       endif
     endif
   endfor
@@ -69,8 +72,16 @@ function! gitgutter#disable() abort
 endfunction
 
 function! gitgutter#enable() abort
+  for bufnr in range(1, bufnr('$') + 1)
+    if buflisted(bufnr)
+      let file = expand('#'.bufnr.':p')
+      if !empty(file)
+        call gitgutter#buffer_enable(bufnr)
+      endif
+    endif
+  endfor
+
   let g:gitgutter_enabled = 1
-  call gitgutter#all(1)
 endfunction
 
 function! gitgutter#toggle() abort
@@ -82,23 +93,24 @@ function! gitgutter#toggle() abort
 endfunction
 
 
-function! gitgutter#buffer_disable() abort
-  let bufnr = bufnr('')
+function! gitgutter#buffer_disable(...) abort
+  let bufnr = a:0 ? a:1 : bufnr('')
   call gitgutter#utility#setbufvar(bufnr, 'enabled', 0)
   call s:clear(bufnr)
 endfunction
 
-function! gitgutter#buffer_enable() abort
-  let bufnr = bufnr('')
+function! gitgutter#buffer_enable(...) abort
+  let bufnr = a:0 ? a:1 : bufnr('')
   call gitgutter#utility#setbufvar(bufnr, 'enabled', 1)
   call gitgutter#process_buffer(bufnr, 1)
 endfunction
 
-function! gitgutter#buffer_toggle() abort
-  if gitgutter#utility#getbufvar(bufnr(''), 'enabled', 1)
-    call gitgutter#buffer_disable()
+function! gitgutter#buffer_toggle(...) abort
+  let bufnr = a:0 ? a:1 : bufnr('')
+  if gitgutter#utility#getbufvar(bufnr, 'enabled', 1)
+    call gitgutter#buffer_disable(bufnr)
   else
-    call gitgutter#buffer_enable()
+    call gitgutter#buffer_enable(bufnr)
   endif
 endfunction
 

autoload/gitgutter/utility.vim

@@ -48,8 +48,7 @@ endfunction
 " Returns truthy when the buffer's file should be processed; and falsey when it shouldn't.
 " This function does not and should not make any system calls.
 function! gitgutter#utility#is_active(bufnr) abort
-  return g:gitgutter_enabled &&
-        \ gitgutter#utility#getbufvar(a:bufnr, 'enabled', 1) &&
+  return gitgutter#utility#getbufvar(a:bufnr, 'enabled') &&
         \ !pumvisible() &&
         \ s:is_file_buffer(a:bufnr) &&
         \ s:exists_file(a:bufnr) &&