refactor: Remove some useless casts

Can't actually enable Wuseless-cast though because Qt's MOC-generated code is
full of them.

src/chatlog/chatline.cpp

@@ -49,7 +49,7 @@ void ChatLine::visibilityChanged(bool visible)
 
 ChatLineContent* ChatLine::getContent(int col) const
 {
-    if (col < static_cast<int>(content.size()) && col >= 0)
+    if (col < content.size() && col >= 0)
         return content[col];
 
     return nullptr;
@@ -145,7 +145,7 @@ void ChatLine::addColumn(ChatLineContent* item, ColumnFormat fmt)
 
 void ChatLine::replaceContent(int col, ChatLineContent* lineContent)
 {
-    if (col >= 0 && col < static_cast<int>(content.size()) && lineContent) {
+    if (col >= 0 && col < content.size() && lineContent) {
         QGraphicsScene* scene = content[col]->scene();
         delete content[col];
 

src/core/core.cpp

@@ -1670,7 +1670,7 @@ uint32_t Core::joinGroupchat(const GroupInvite& inviteInfo)
     case TOX_CONFERENCE_TYPE_AV: {
         qDebug() << QString("Trying to join AV groupchat invite sent by friend %1").arg(friendId);
         groupNum = toxav_join_av_groupchat(tox.get(), friendId, cookie, cookieLength,
-                                           CoreAV::groupCallCallback, const_cast<Core*>(this));
+                                           CoreAV::groupCallCallback, this);
         break;
     }
     default:

src/model/sessionchatlog.cpp

@@ -98,7 +98,7 @@ std::map<ChatLogIdx, ChatLogItem>::const_iterator
 firstItemAfterDate(QDate date, const std::map<ChatLogIdx, ChatLogItem>& items)
 {
 #if (QT_VERSION >= QT_VERSION_CHECK(5, 15, 0))
-    return std::lower_bound(items.begin(), items.end(), QDateTime(date.startOfDay()),
+    return std::lower_bound(items.begin(), items.end(), date.startOfDay(),
 #else
     return std::lower_bound(items.begin(), items.end(), QDateTime(date),
 #endif