wxGUI/gcmd: fix read command stdout (#1228)

(caused an incorrect line break in the e.g. 'GRASS_INFO_PERCENT: 3'
and error during parsing percent value)

gui/wxpython/core/gcmd.py

@@ -297,7 +297,7 @@ class Popen(subprocess.Popen):
                 if not select.select([conn], [], [], 0)[0]:
                     return ''
 
-                r = conn.read(maxsize)
+                r = conn.read()
 
                 if not r:
                     return self._close(which)