buildhistory.bbclass: restore BUILDHISTORY_PRESERVE files

On each build using sstate-cache, buildhistory will move
content to a temporary folder named `old`.
When buildhistory looks for the main dir, it wont find it
and ends up creating it.
As a consequence how code is structured wont restore any
preserved file.

Code block moved to ensure if old dir exists, it will
attempt to restore those files marked to preserve.

Signed-off-by: Pedro Silva Ferreira <Pedro.Silva.Ferreira@criticaltechworks.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

Author: Pedro Ferreira

meta/classes/buildhistory.bbclass

@@ -260,14 +260,6 @@ python buildhistory_emit_pkghistory() {
     if not os.path.exists(pkghistdir):
         bb.utils.mkdirhier(pkghistdir)
     else:
-        # We need to make sure that all files kept in
-        # buildhistory/old are restored successfully
-        # otherwise next block of code wont have files to
-        # check and purge
-        if d.getVar("BUILDHISTORY_RESET"):
-            for pkg in packagelist:
-                preservebuildhistoryfiles(pkg, preserve)
-
         # Remove files for packages that no longer exist
         for item in os.listdir(pkghistdir):
             if item not in preserve:
@@ -280,6 +272,13 @@ python buildhistory_emit_pkghistory() {
                     else:
                         os.unlink(itempath)
 
+    if os.path.exists(oldpkghistdir):
+        # We need to make sure that all files in preserve
+        # are restored from buildhistory/old successfully
+        if d.getVar("BUILDHISTORY_RESET"):
+            for pkg in packagelist:
+                preservebuildhistoryfiles(pkg, preserve)
+
     rcpinfo = RecipeInfo(pn)
     rcpinfo.pe = pe
     rcpinfo.pv = pv