gptel-transient: No pre-fill when reading from minibuffer

* gptel-transient.el (gptel--suffix-send): Don't pre-fill the
minibuffer prompt with the current line when reading the query
from the minibuffer.  (If the region is active, it is used as the
initial contents -- this behavior is unchanged.)

gptel-transient.el

@@ -599,10 +599,9 @@ Or in an extended conversation:
           ((member "m" args)
            (read-string
             (format "Ask %s: " (gptel-backend-name gptel-backend))
-            (apply #'buffer-substring-no-properties
-                   (if (use-region-p)
-                       (list (region-beginning) (region-end))
-                     (list (line-beginning-position) (line-end-position))))))
+            (and (use-region-p)
+                 (buffer-substring-no-properties
+                  (region-beginning) (region-end)))))
           ((member "y" args)
            (unless (car-safe kill-ring)
              (user-error "`kill-ring' is empty!  Nothing to send"))