[macOS, CI] Do not upload a nightly if there's already one of the same commit

CI/deploy.osx.sh

@@ -6,4 +6,6 @@ DATE=`date +'%d%m%Y'`
 SHORT_COMMIT=`git rev-parse --short ${TRAVIS_COMMIT}`
 TARGET_FILENAME="OpenMW-${DATE}-${SHORT_COMMIT}.dmg"
 
-curl --ssl --ftp-create-dirs -T *.dmg -u $OSX_FTP_USER:$OSX_FTP_PASSWORD "${OSX_FTP_URL}${TARGET_FILENAME}"
+if ! curl --ssl -u $OSX_FTP_USER:$OSX_FTP_PASSWORD "${OSX_FTP_URL}" --silent | grep $SHORT_COMMIT > /dev/null; then
+    curl --ssl --ftp-create-dirs -T *.dmg -u $OSX_FTP_USER:$OSX_FTP_PASSWORD "${OSX_FTP_URL}${TARGET_FILENAME}"
+fi