Check tmux exists before loading osc52

vimrc

@@ -36,10 +36,7 @@ endfor
 Pack 'mkitt/tabline.vim'
 
 " YouCompleteMe
-" TODO: Try out neovim completion plugins to see if they are better
-if !platform#is_windows()
-  Pack 'ycm-core/YouCompleteMe',
-    \ {'type': 'opt', 'do': '!./install.py --clang-completer'}
+Pack 'ycm-core/YouCompleteMe', {'type': 'opt'}
 let g:ycm_key_list_select_completion = ['<C-n>', '<Down>']
 let g:ycm_key_list_previous_completion = ['<C-p>', '<Up>']
 let g:ycm_min_num_of_chars_for_completion = 1
@@ -53,7 +50,7 @@ if !platform#is_windows()
 let g:ycm_warning_symbol = '▸'
 let g:ycm_goto_buffer_command = 'horizontal-split'
 let g:ycm_use_clangd = 0
-endif
+
 " ultisnips - snippet engine
 Pack 'SirVer/ultisnips'
 Pack 'honza/vim-snippets'
@@ -203,7 +200,8 @@ Pack 'jrozner/vim-antlr'
 
 " Plugins for remote integrations
 Pack 'greymd/oscyank.vim', {'type': 'opt'}
-let g:use_osc52 = trim(system('tmux show-options -g set-clipboard')) ==# 'set-clipboard on'
+let g:use_osc52 = $TMUX !=# '' &&
+\ trim(system('tmux show-options -g set-clipboard')) ==# 'set-clipboard on'
 if g:use_osc52
   packadd oscyank.vim
 endif