vim-patch:62ccaa6: runtime(termdebug): check for gdb file/dir before using as buffer name (#28908)

Add test so that this doesn't regress.

fixes: vim/vim#12718
closes: vim/vim#14792

https://github.com/vim/vim/commit/62ccaa60d5f7f9a13c758bd5e55b7ca6855a6de9

Co-authored-by: Ubaldo Tiberi <ubaldo.tiberi@volvo.com>

runtime/pack/dist/opt/termdebug/plugin/termdebug.vim

@@ -427,7 +427,17 @@ func s:StartDebug_prompt(dict)
   let s:promptbuf = bufnr('')
   call prompt_setprompt(s:promptbuf, 'gdb> ')
   set buftype=prompt
-  file gdb
+
+  if empty(glob('gdb'))
+    file gdb
+  elseif empty(glob('Termdebug-gdb-console'))
+    file Termdebug-gdb-console
+  else
+    call s:Echoerr("You have a file/folder named 'gdb'
+          \ or 'Termdebug-gdb-console'.
+          \ Please exit and rename them because Termdebug may not work as expected.")
+  endif
+
   call prompt_setcallback(s:promptbuf, function('s:PromptCallback'))
   call prompt_setinterrupt(s:promptbuf, function('s:PromptInterrupt'))
 
@@ -1481,9 +1491,12 @@ func s:GotoAsmwinOrCreateIt()
 
     if s:asmbuf > 0 && bufexists(s:asmbuf)
       exe 'buffer' . s:asmbuf
-    else
+    elseif empty(glob('Termdebug-asm-listing'))
       silent file Termdebug-asm-listing
       let s:asmbuf = bufnr('Termdebug-asm-listing')
+    else
+      call s:Echoerr("You have a file/folder named 'Termdebug-asm-listing'.
+          \ Please exit and rename it because Termdebug may not work as expected.")
     endif
 
     if mdf != 'vert' && s:GetDisasmWindowHeight() > 0
@@ -1550,9 +1563,12 @@ func s:GotoVariableswinOrCreateIt()
 
     if s:varbuf > 0 && bufexists(s:varbuf)
       exe 'buffer' . s:varbuf
-    else
+    elseif empty(glob('Termdebug-variables-listing'))
       silent file Termdebug-variables-listing
       let s:varbuf = bufnr('Termdebug-variables-listing')
+    else
+      call s:Echoerr("You have a file/folder named 'Termdebug-variables-listing'.
+          \ Please exit and rename it because Termdebug may not work as expected.")
     endif
 
     if mdf != 'vert' && s:GetVariablesWindowHeight() > 0