abiword: add patch to fix incompatibility with musl NULL

srcpkgs/abiword/patches/musl.patch

@@ -0,0 +1,11 @@
+--- a/src/af/xap/xp/xap_Dialog.cpp	2021-07-03 17:46:07.000000000 +0200
++++ -	2023-02-23 13:21:03.557255506 +0100
+@@ -267,7 +267,7 @@
+ // This function constructs and returns the window name of a modeless dialog by
+ // concatenating the active frame with the dialog name
+ 
+-	*pWindowName = (char) NULL;
++	*pWindowName = '\0';
+ 	UT_UTF8String wn = UT_UTF8String(pDialogName);
+ 
+ 	XAP_Frame* pFrame = getActiveFrame();