[console] Add a function to clear the scroll-back buffer

Needed for when the console display is cleared.

include/QF/console.h

@@ -98,6 +98,7 @@ con_buffer_t *Con_CreateBuffer (size_t buffer_size, int max_lines);
 void Con_DestroyBuffer (con_buffer_t *buffer);
 void Con_BufferAddText (con_buffer_t *buf, const char *text);
 #define Con_BufferLine(b,l) ((b)->lines + ((l) + (b)->max_lines) % (b)->max_lines)
+void Con_ClearBuffer (con_buffer_t *buffer);
 
 // init/shutdown functions
 void Con_Init (const char *plugin_name);

libs/console/buffer.c

@@ -125,3 +125,12 @@ Con_BufferAddText (con_buffer_t *buf, const char *text)
 		}
 	}
 }
+
+VISIBLE void
+Con_ClearBuffer (con_buffer_t *buffer)
+{
+	buffer->line_head = 1;
+	buffer->line_tail = 0;
+	buffer->lines[0].text = 0;
+	buffer->lines[0].len = 0;
+}