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.

(From OE-Core rev: 0f8c6e6bc783de248ed346607541d26567f18858)

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