patch 8.2.1191: Vim9: crash when function calls itself

Problem:    Vim9: crash when function calls itself.
Solution:   Add status UF_COMPILING. (closes #6441)
diff --git a/src/structs.h b/src/structs.h
index bdc763b..4a0c10a 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1539,6 +1539,7 @@
 typedef enum {
     UF_NOT_COMPILED,
     UF_TO_BE_COMPILED,
+    UF_COMPILING,
     UF_COMPILED
 } def_status_T;
 
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 5ea2945..53206df 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -999,5 +999,17 @@
   call delete('XTest_silent_echo')
 endfunc
 
+def Fibonacci(n: number): number
+  if n < 2
+    return n
+  else
+    return Fibonacci(n - 1) + Fibonacci(n - 2)
+  endif
+enddef
+
+def Test_recursive_call()
+  assert_equal(6765, Fibonacci(20))
+enddef
+
 
 " vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker
diff --git a/src/version.c b/src/version.c
index 8ae2f29..487303e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1191,
+/**/
     1190,
 /**/
     1189,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index fceb481..8d6c139 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -6802,6 +6802,8 @@
     else if (add_def_function(ufunc) == FAIL)
 	return FAIL;
 
+    ufunc->uf_def_status = UF_COMPILING;
+
     CLEAR_FIELD(cctx);
     cctx.ctx_ufunc = ufunc;
     cctx.ctx_lnum = -1;