FIX: Disable overlay scrollbar under GTK2

src/doublecmd.lpi

@@ -204,7 +204,7 @@
         <PackageName Value="viewerpackage"/>
       </Item7>
     </RequiredPackages>
-    <Units Count="151">
+    <Units Count="152">
       <Unit0>
         <Filename Value="doublecmd.lpr"/>
         <IsPartOfProject Value="True"/>
@@ -1153,6 +1153,11 @@
         <ResourceBaseClass Value="Frame"/>
         <UnitName Value="fOptionsDrivesListButton"/>
       </Unit150>
+      <Unit151>
+        <Filename Value="platform\unix\uoverlayscrollbarfix.pas"/>
+        <IsPartOfProject Value="True"/>
+        <UnitName Value="uOverlayScrollBarFix"/>
+      </Unit151>
     </Units>
   </ProjectOptions>
   <CompilerOptions>

src/doublecmd.lpr

@@ -8,6 +8,9 @@ uses
   cthreads,
   //cwstring,
   clocale,
+  {$IFDEF LCLGTK2}
+  uOverlayScrollBarFix,
+  {$ENDIF}
   {$ENDIF}
   Interfaces,
   LCLProc,
@@ -125,4 +128,4 @@ begin
 
   uKeyboard.CleanupKeyboard;
   DCDebug('Finished Double Commander');
-end.
+end.

src/platform/unix/uoverlayscrollbarfix.pas

@@ -0,0 +1,14 @@
+unit uOverlayScrollBarFix; 
+
+{$mode objfpc}{$H+}
+
+interface
+
+implementation
+
+  function setenv(const name, value: pchar; overwrite: longint): longint; cdecl; external 'c' name 'setenv';
+
+initialization
+  setenv('LIBOVERLAY_SCROLLBAR', '0', 1);
+
+end.