patch 8.2.3208: dynamic library load error does not mention why it failed

Problem:    Dynamic library load error does not mention why it failed.
Solution:   Add the error message. (Martin Tournoij, closes #8621)
diff --git a/src/if_mzsch.c b/src/if_mzsch.c
index 0c1c765..c8be940 100644
--- a/src/if_mzsch.c
+++ b/src/if_mzsch.c
@@ -668,14 +668,14 @@
     if (!hMzGC)
     {
 	if (verbose)
-	    semsg(_(e_loadlib), gc_dll);
+	    semsg(_(e_loadlib), gc_dll, GetWin32Error());
 	return FAIL;
     }
 
     if (!hMzSch)
     {
 	if (verbose)
-	    semsg(_(e_loadlib), sch_dll);
+	    semsg(_(e_loadlib), sch_dll, GetWin32Error());
 	return FAIL;
     }