patch 8.1.2145: cannot map <C-H> when modifyOtherKeys is enabled

Problem:    Cannot map <C-H> when modifyOtherKeys is enabled.
Solution:   Add the <C-H> mapping twice, both with modifier and as 0x08.  Use
            only the first one when modifyOtherKeys has been detected.
diff --git a/src/gui_w32.c b/src/gui_w32.c
index 61b09e1..ae47873 100644
--- a/src/gui_w32.c
+++ b/src/gui_w32.c
@@ -850,7 +850,7 @@
 	modifiers &= ~MOD_MASK_SHIFT;
 
     /* Interpret the ALT key as making the key META, include SHIFT, etc. */
-    ch = extract_modifiers(ch, &modifiers);
+    ch = extract_modifiers(ch, &modifiers, TRUE, NULL);
     if (ch == CSI)
 	ch = K_CSI;