patch 8.2.2989: Vim9: memory leak when debugging a :def function

Problem:    Vim9: memory leak when debugging a :def function.
Solution:   Free the debug instructions.
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 1747f30..be8f304 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -10045,6 +10045,13 @@
 	VIM_CLEAR(dfunc->df_instr);
 	dfunc->df_instr = NULL;
     }
+    if (dfunc->df_instr_debug != NULL)
+    {
+	for (idx = 0; idx < dfunc->df_instr_debug_count; ++idx)
+	    delete_instr(dfunc->df_instr_debug + idx);
+	VIM_CLEAR(dfunc->df_instr_debug);
+	dfunc->df_instr_debug = NULL;
+    }
 #ifdef FEAT_PROFILE
     if (dfunc->df_instr_prof != NULL)
     {