patch 8.2.3673: crash when allocating signal stack fails

Problem:    Crash when allocating signal stack fails.
Solution:   Only using sourcing info when available. (closes #9215)
diff --git a/src/globals.h b/src/globals.h
index 90998d8..8f4f5a5 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -288,6 +288,7 @@
  * Current context is at ga_len - 1.
  */
 EXTERN garray_T	exestack INIT5(0, 0, sizeof(estack_T), 50, NULL);
+#define HAVE_SOURCING_INFO  (exestack.ga_data != NULL && exestack.ga_len > 0)
 // name of error message source
 #define SOURCING_NAME (((estack_T *)exestack.ga_data)[exestack.ga_len - 1].es_name)
 // line number in the message source or zero
diff --git a/src/message.c b/src/message.c
index 0cd09da..e438211 100644
--- a/src/message.c
+++ b/src/message.c
@@ -446,7 +446,7 @@
     static int
 other_sourcing_name(void)
 {
-    if (SOURCING_NAME != NULL)
+    if (HAVE_SOURCING_INFO && SOURCING_NAME != NULL)
     {
 	if (last_sourcing_name != NULL)
 	    return STRCMP(SOURCING_NAME, last_sourcing_name) != 0;
@@ -465,7 +465,7 @@
 {
     char_u	*Buf, *p;
 
-    if (SOURCING_NAME != NULL && other_sourcing_name())
+    if (HAVE_SOURCING_INFO && SOURCING_NAME != NULL && other_sourcing_name())
     {
 	char_u	    *sname = estack_sfile(ESTACK_NONE);
 	char_u	    *tofree = sname;
diff --git a/src/version.c b/src/version.c
index d1004bb..3f83103 100644
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3673,
+/**/
     3672,
 /**/
     3671,