Allow loading from reaper's system-wide plugin path

[dvzrv]

Hi! 👋

When upgrading the Arch Linux package to 1.2.4.5 I noticed, that we have the user manually symlink the plugin into place (https://gitlab.archlinux.org/archlinux/packaging/packages/reapack/-/blob/519fb6d0af1f98d0672fd5c5e88b0e254bbe2ef0/reapack.install).

This appears to be due to

reapack/src/main.cpp

Lines 91 to 124 in 1727aa3

	static bool checkLocation(REAPER_PLUGIN_HINSTANCE module)
	{
	// using FS::canonical is required on macOS Catalina and newer,
	// whose dladdr automatically resolves symbolic links from the module's path
	Path expected;
	expected.append(ReaPack::resourcePath());
	expected.append("UserPlugins");
	expected.append(REAPACK_FILENAME);
	expected = FS::canonical(expected);
	#ifdef _WIN32
	Win32::char_type self[MAX_PATH]{};
	GetModuleFileName(module, self, static_cast<DWORD>(std::size(self)));
	const Path current(Win32::narrow(self));
	#else
	Dl_info info{};
	dladdr(reinterpret_cast<const void *>(&checkLocation), &info);
	const Path &current = FS::canonical({info.dli_fname});
	#endif
	if(current == expected)
	return true;
	Win32::messageBox(Splash_GetWnd(), String::format(
	"ReaPack was not loaded from the standard extension path"
	" or its filename was altered.\n"
	"Move or rename it to the expected location and retry.\n\n"
	"Current: %s\n\nExpected: %s",
	current.join().c_str(), expected.join().c_str()
	).c_str(), "ReaPack: Installation path mismatch", MB_OK);
	return false;
	}

Is that a requirement by reaper itself?

If I remove this check, e.g.:

diff --git i/src/main.cpp w/src/main.cpp
index de93e98..cd967c2 100644
--- i/src/main.cpp
+++ w/src/main.cpp
@@ -109,18 +109,7 @@ static bool checkLocation(REAPER_PLUGIN_HINSTANCE module)
   const Path &current = FS::canonical({info.dli_fname});
 #endif

-  if(current == expected)
-    return true;
-
-  Win32::messageBox(Splash_GetWnd(), String::format(
-    "ReaPack was not loaded from the standard extension path"
-    " or its filename was altered.\n"
-    "Move or rename it to the expected location and retry.\n\n"
-    "Current: %s\n\nExpected: %s",
-    current.join().c_str(), expected.join().c_str()
-  ).c_str(), "ReaPack: Installation path mismatch", MB_OK);
-
-  return false;
+  return true;
 }

 extern "C" REAPER_PLUGIN_DLL_EXPORT int REAPER_PLUGIN_ENTRYPOINT(

I am able to start reaper and the plugin is found automatically, if I place it below /usr/lib/REAPER/Plugins/ (that's where/ how we package reaper on Arch Linux).