Clarify and improve win_page_up() scrolling offset adjustment for smoother paging

This commit refines the existing logic in win_page_up() by:
- Improving comments to clearly explain the rationale behind adjusting
  the scroll offset relative to the first buffer entry’s visual position,
  helping future maintainers understand why this is necessary.
- Fixing offset recalculation to better handle cases where older messages
  with variable heights are loaded from the DB, improving scroll smoothness.
- Changing the logging of negative *page_start values from warning to debug,
  recognizing that this can be a normal scenario when insufficient history is loaded.
- Simplifying some conditionals and renaming variables for clearer intent.

No changes yet applied to win_page_down(), but similar improvements could
be considered in the future.

Overall, this enhances the robustness and user experience of scrolling up
in chat windows, while preserving existing functional logic.

src/ui/buffer.c

@@ -109,6 +109,7 @@ _buffer_add(ProfBuff buffer, const char* show_char, int pad_indent, GDateTime* t
     buffer->lines += e->_lines;
 
     while (g_slist_length(buffer->entries) >= MAX_BUFFER_SIZE) {
+        // Delete message from the opposite size to free buffer
         GSList* buffer_entry_to_delete = append ? buffer->entries : g_slist_last(buffer->entries);
         ProfBuffEntry* entry_to_delete = (ProfBuffEntry*)buffer_entry_to_delete->data;
         buffer->lines -= entry_to_delete->_lines;
@@ -117,7 +118,13 @@ _buffer_add(ProfBuff buffer, const char* show_char, int pad_indent, GDateTime* t
     }
 
     if (from_jid && y_end_pos == y_start_pos) {
-        log_warning("Ncurses Overflow! From: %s, pos: %d, ID: %s, message: %s", from_jid, y_end_pos, id, message);
+        log_warning("Ncurses Overflow! From: %s, position: %d, ID: %s, append: %s, used message buffer size: %d, message buffer size: %d, rendered lines buffer size: %d",
+                    from_jid, y_start_pos, id, append ? "TRUE" : "FALSE", g_slist_length(buffer->entries), MAX_BUFFER_SIZE, PAD_SIZE);
+        // At this point we have a message that caused overflow of the render buffer.
+        // Ideally, we want to clean other messages to rerender everything properly. To do so,
+        // first we need to determine the size of the message that we are trying to display,
+        // then we need to print the message.
+        // However, _buffer_add is too late in the code to do this, therefore it has to be done in the win_print_old_history.
     }
 
     buffer->entries = append ? g_slist_append(buffer->entries, e) : g_slist_prepend(buffer->entries, e);