[YouTube] Do not get twice runs array in YoutubeParsingHelper

The runs object was computed twice in getTextFromObject and getUrlFromObject
methods, leading to unneeded search costs. This has been avoided by storing the
array in method variables.

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeParsingHelper.java

@@ -892,12 +892,13 @@ public final class YoutubeParsingHelper {
             return textObject.getString("simpleText");
         }
 
-        if (textObject.getArray("runs").isEmpty()) {
+        final JsonArray runs = textObject.getArray("runs");
+        if (runs.isEmpty()) {
             return null;
         }
 
         final StringBuilder textBuilder = new StringBuilder();
-        for (final Object o : textObject.getArray("runs")) {
+        for (final Object o : runs) {
             final JsonObject run = (JsonObject) o;
             String text = run.getString("text");
 
@@ -975,11 +976,12 @@ public final class YoutubeParsingHelper {
             return null;
         }
 
-        if (textObject.getArray("runs").isEmpty()) {
+        final JsonArray runs = textObject.getArray("runs");
+        if (runs.isEmpty()) {
             return null;
         }
 
-        for (final Object textPart : textObject.getArray("runs")) {
+        for (final Object textPart : runs) {
             final String url = getUrlFromNavigationEndpoint(((JsonObject) textPart)
                     .getObject("navigationEndpoint"));
             if (!isNullOrEmpty(url)) {