vim-patch:8.2.4541: Crash in debugger when a variable is not available

Problem:    Crash in debugger when a variable is not available in the current
            block.
Solution:   Check for a NULL name. (closes vim/vim#9926)

e406ff87c8

Co-authored-by: Bram Moolenaar <Bram@vim.org>

test/old/testdir/test_debugger.vim

@@ -73,6 +73,13 @@ func Test_Debugger()
 	  endtry
 	  return var1
 	endfunc
+        def Vim9Func()
+          for cmd in ['confirm', 'xxxxxxx']
+            for _ in [1, 2]
+              echo cmd
+            endfor
+          endfor
+        enddef
   END
   call writefile(lines, 'Xtest.vim')
 
@@ -298,6 +305,14 @@ func Test_Debugger()
 	      \ 'line 5: catch'])
   call RunDbgCmd(buf, 'c')
 
+  " Test showing local variable in :def function
+  call RunDbgCmd(buf, ':breakadd func 2 Vim9Func')
+  call RunDbgCmd(buf, ':call Vim9Func()', ['line 2:             for _ in [1, 2]'])
+  call RunDbgCmd(buf, 'next', ['line 2: for _ in [1, 2]'])
+  call RunDbgCmd(buf, 'echo cmd', ['confirm'])
+  call RunDbgCmd(buf, 'breakdel *')
+  call RunDbgCmd(buf, 'cont')
+
   " Test for :quit
   call RunDbgCmd(buf, ':debug echo Foo()')
   call RunDbgCmd(buf, 'breakdel *')