fix: comparison of integers of different signs (#6749)

The `targetIndex` (`int`) was compared to `maxIndex` (`size_t`). This
generated a large warning, because it was in a lambda. Since we parse
`targetIndex`, we can parse it as a `size_t`.

src/controllers/commands/builtin/twitch/Prediction.cpp

@@ -280,7 +280,7 @@ QString completePrediction(const CommandContext &ctx)
         return "";
     }
 
-    int targetIndex = 0;
+    size_t targetIndex = 0;
     QString targetName;
     if (hasName)
     {
@@ -289,8 +289,8 @@ QString completePrediction(const CommandContext &ctx)
     else
     {
         bool ok = true;
-        targetIndex = parser.value(indexOption).toInt(&ok);
-        if (!ok || targetIndex <= 0)
+        targetIndex = parser.value(indexOption).toULongLong(&ok);
+        if (!ok || targetIndex == 0)
         {
             ctx.channel->addSystemMessage("Invalid index - " + usage);
             return "";