Fix seg faul when parsing invalid <plurals>

If the inner element of a <plurals> tag fails to parse, aapt2 will seg
fault. Don't do that.

Bug: 123423125
Test: manual
Change-Id: Iff39fa84073da62d85279683ac3d03b7309bc5e3

tools/aapt2/ResourceParser.cpp

@@ -1623,7 +1623,9 @@ bool ResourceParser::ParsePlural(xml::XmlPullParser* parser,
       if (!(plural->values[index] = ParseXml(
                 parser, android::ResTable_map::TYPE_STRING, kNoRawString))) {
         error = true;
+        continue;
       }
+
       plural->values[index]->SetSource(item_source);
 
     } else if (!ShouldIgnoreElement(element_namespace, element_name)) {