shared/gui: Don't consider non-content search results for previews

Not entirely ideal, since we may want to search for 'cake', and look at
a preview for 'cake.txt' even if there is no 'cake' inside.

But this will do for now

shared/searchresult.h

@@ -7,6 +7,7 @@ class SearchResult
   public:
 	FileData fileData;
 	QVector<unsigned int> pages;
+	bool wasContentSearch = false;
 };
 
 #endif // SEARCHRESULT_H