contrib: check for unsigned apk in release.sh

release.sh expects signed apks. if a non-releasemanager uses
release.sh to build it will build the apks unsigned and then
rename them to the same name as the signed apks. However
if the apks have already been built separately and are still named
*-unsigned.apk it will not detect them and instead try to build them
again. Instead it should just rename them to *-release.apk as if built
directly through release.sh.

contrib/release.sh

@@ -164,7 +164,12 @@ do
         if [ ! -z "$RELEASEMANAGER" ] ; then
             ./contrib/android/build.sh qml $arch release $password
         else
-            ./contrib/android/build.sh qml $arch release-unsigned
+            if test -f "dist/$apk_unsigned"; then
+                # has already been built separately before
+                info "found unsigned: $apk_unsigned"
+            else
+                ./contrib/android/build.sh qml $arch release-unsigned
+            fi
             mv "dist/$apk_unsigned" "dist/$apk"
         fi
     fi