fix output of merge_js

misc/merge_js.sh

@@ -51,7 +51,7 @@ _create_jsheader () {
       </xsl:attribute>
     </xsl:element>
     "
-        sed -i "s|^\(.*JS_INCLUDE.*\)$|    <script src=\"${DIST_BUNDLE}\"><\/script>\n\1|g" public/index.html ;
+        [[ -f "public/index.html" ]] && sed -i "s|^\(.*JS_INCLUDE.*\)$|    <script src=\"${DIST_BUNDLE}\"><\/script>\n\1|g" public/index.html ;
     else
         _ALL_SOURCES=$@
         echo "${_ALL_SOURCES}"