update bug 1807834 patch

mozilla-central/patches/1807834-respect-dmg-hfs-env.patch

@@ -38,13 +38,13 @@ diff --git a/python/mozbuild/mozbuild/action/make_dmg.py b/python/mozbuild/mozbu
 -    hfs_tool = bootstrap_toolchain("dmg/hfsplus")
 -    mkfshfs_tool = bootstrap_toolchain("hfsplus/newfs_hfs")
 +    dmg_tool = buildconfig.substs.get("DMG_TOOL")
-+    if dmg_tool == "":
++    if dmg_tool is None:
 +        dmg_tool = bootstrap_toolchain("dmg/dmg")
 +    hfs_tool = buildconfig.substs.get("HFS_TOOL")
-+    if hfs_tool == "":
++    if hfs_tool is None:
 +        hfs_tool = bootstrap_toolchain("dmg/hfsplus")
 +    mkfshfs_tool= buildconfig.substs.get("MKFSHFS")
-+    if mkfshfs_tool == "":
++    if mkfshfs_tool is None:
 +        mkfshfs_tool = bootstrap_toolchain("hfsplus/newfs_hfs")
  
      dmg.create_dmg(