freeimage: fix building on musl

srcpkgs/freeimage/patches/fix-musl.patch

@@ -0,0 +1,19 @@
+Fixes following compile error due to musl using nullptr instead of __null:
+
+Source/FreeImage/PluginPSD.cpp: In function ‘BOOL Save(FreeImageIO*, FIBITMAP*, fi_handle, int, int, void*)’:
+Source/FreeImage/PluginPSD.cpp:130:10: error: cannot convert ‘std::nullptr_t’ to ‘BOOL’ {aka ‘int’} in return
+  130 |   return NULL;
+      |          ^~~~
+
+diff -rup Source/FreeImage/PluginPSD.cpp.orig Source/FreeImage/PluginPSD.cpp
+--- a/Source/FreeImage/PluginPSD.cpp
++++ b/Source/FreeImage/PluginPSD.cpp
+@@ -127,7 +127,7 @@ Load(FreeImageIO *io, fi_handle handle,
+ static BOOL DLL_CALLCONV
+ Save(FreeImageIO *io, FIBITMAP *dib, fi_handle handle, int page, int flags, void *data) {
+ 	if(!handle) {
+-		return NULL;
++		return FALSE;
+ 	}
+ 	try {
+ 		psdParser parser;