Fix tag extraction.

Attempted to read deleted memory.

src/cgi.cpp

@@ -31,6 +31,7 @@
 #include <sstream>
 #include <stdexcept>
 #include <string>
+#include <string_view>
 #include <vector>
 
 namespace FediBlock::cgi
@@ -112,7 +113,7 @@ vector<string> get_tags()
     cgi.getElement("tags[]", tags_form);
     for (const auto &element : tags_form)
     {
-        const string_view tag{element.getValue()};
+        const string tag{element.getValue()};
         if (!tag.empty())
         {
             tags_string.push_back(tolower(tag));