Fix AppImage shim launcher

Due to upstream change in linuxdeployqt

cmake/linux/package_linux.sh.in

@@ -55,6 +55,7 @@ echo -e "\nWriting verbose output to \"${LOGFILE}\""
 export PATH="$(pwd -P)/squashfs-root/usr/bin:$(dirname "@QT_QMAKE_EXECUTABLE@")":$PATH
 
 # Fetch portable linuxdeployqt if cache is older than $DAYSOLD
+APPIMAGETOOL="squashfs-root/usr/bin/appimagetool"
 echo -e "\nDownloading linuxdeployqt to ${LINUXDEPLOYQT}..."
 mkdir -p "$HOME/bin"
 DAYSOLD=2
@@ -69,7 +70,6 @@ elif ! find "$LINUXDEPLOYQT" -mtime -$DAYSOLD 2>/dev/null|grep -q "." > /dev/nul
 	touch "$LINUXDEPLOYQT"
 	success "Downloaded $LINUXDEPLOYQT"
 	"$LINUXDEPLOYQT" --appimage-extract > /dev/null 2>&1
-	APPIMAGETOOL="squashfs-root/usr/bin/appimagetool"
 	success "Extracted $APPIMAGETOOL"
 else
 	skipped "$LINUXDEPLOYQT is less than $DAYSOLD days old"
@@ -181,6 +181,10 @@ if [ -e "${APPDIR}/usr/lib/libjack.so.0" ]; then
    mv "${APPDIR}/usr/lib/libjack.so.0" "${APPDIR}usr/lib/lmms/optional/"
 fi
 
+# Point the AppRun to the shim launcher
+rm -f "${APPDIR}/AppRun"
+ln -sr "${APPDIR}/usr/bin/lmms" "${APPDIR}/AppRun"
+
 # Create AppImage
 echo -e "\nFinishing the AppImage..."
 echo -e "\n\n>>>>> appimagetool" >> "$LOGFILE"