lua: Handle file dialogs completely on main gui thread

wx doesn't seem to like the dialogs being created on some other worker
thread, which makes file dialogs opened by lua scripts crash in various
ways on Linux. Doing everything on the main thread hopefully fixes this.

Fixes TypesettingTools#51 .

Author: arch1t3cht

src/auto4_base.cpp

@@ -221,13 +221,6 @@ namespace Automation4 {
 		});
 	}
 
-	int ProgressSink::ShowDialog(wxDialog *dialog)
-	{
-		int ret = 0;
-		agi::dispatch::Main().Sync([&] { ret = dialog->ShowModal(); });
-		return ret;
-	}
-
 	BackgroundScriptRunner::BackgroundScriptRunner(wxWindow *parent, std::string const& title)
 	: impl(new DialogProgress(parent, to_wx(title)))
 	{

src/auto4_base.h

@@ -132,7 +132,6 @@ namespace Automation4 {
 		/// Show the passed dialog on the GUI thread, blocking the calling
 		/// thread until it closes
 		void ShowDialog(ScriptDialog *config_dialog);
-		int ShowDialog(wxDialog *dialog);
 		wxWindow *GetParentWindow() const { return bsr->GetParentWindow(); }
 
 		/// Get the current automation trace level

src/auto4_lua_progresssink.cpp

@@ -36,6 +36,7 @@
 
 #include "compat.h"
 
+#include <libaegisub/dispatch.h>
 #include <libaegisub/lua/utils.h>
 
 #include <wx/filedlg.h>
@@ -197,7 +198,6 @@ namespace Automation4 {
 
 	int LuaProgressSink::LuaDisplayOpenDialog(lua_State *L)
 	{
-		ProgressSink *ps = GetObjPointer(L, lua_upvalueindex(1));
 		wxString message(check_wxstring(L, 1));
 		wxString dir(check_wxstring(L, 2));
 		wxString file(check_wxstring(L, 3));
@@ -211,26 +211,24 @@ namespace Automation4 {
 		if (must_exist)
 			flags |= wxFD_FILE_MUST_EXIST;
 
-		wxFileDialog diag(nullptr, message, dir, file, wildcard, flags);
-		if (ps->ShowDialog(&diag) == wxID_CANCEL) {
-			lua_pushnil(L);
-			return 1;
-		}
-
-		if (multiple) {
-			wxArrayString files;
-			diag.GetPaths(files);
-
-			lua_createtable(L, files.size(), 0);
-			for (size_t i = 0; i < files.size(); ++i) {
-				lua_pushstring(L, files[i].utf8_str());
-				lua_rawseti(L, -2, i + 1);
+		agi::dispatch::Main().Sync([&] {
+			wxFileDialog diag(nullptr, message, dir, file, wildcard, flags);
+			if (diag.ShowModal() == wxID_CANCEL) {
+				lua_pushnil(L);
+			} else if (multiple) {
+				wxArrayString files;
+				diag.GetPaths(files);
+
+				lua_createtable(L, files.size(), 0);
+				for (size_t i = 0; i < files.size(); ++i) {
+					lua_pushstring(L, files[i].utf8_str());
+					lua_rawseti(L, -2, i + 1);
+				}
+			} else {
+				lua_pushstring(L, diag.GetPath().utf8_str());
 			}
+		});
 
-			return 1;
-		}
-
-		lua_pushstring(L, diag.GetPath().utf8_str());
 		return 1;
 	}
 
@@ -247,13 +245,15 @@ namespace Automation4 {
 		if (prompt_overwrite)
 			flags |= wxFD_OVERWRITE_PROMPT;
 
-		wxFileDialog diag(ps->GetParentWindow(), message, dir, file, wildcard, flags);
-		if (ps->ShowDialog(&diag) == wxID_CANCEL) {
-			lua_pushnil(L);
-			return 1;
-		}
+		agi::dispatch::Main().Sync([&] {
+			wxFileDialog diag(ps->GetParentWindow(), message, dir, file, wildcard, flags);
+			if (diag.ShowModal() == wxID_CANCEL) {
+				lua_pushnil(L);
+			} else {
+				lua_pushstring(L, diag.GetPath().utf8_str());
+			}
+		});
 
-		lua_pushstring(L, diag.GetPath().utf8_str());
 		return 1;
 	}
 }