* Fix a segfault in rotate_180 on 0 sized canvas

caca/transform.c

@@ -191,6 +191,9 @@ int caca_rotate_180(caca_canvas_t *cv)
     uint32_t *aend = abegin + cv->width * cv->height - 1;
     int y;
 
+    if(!cbegin)
+	return 0;
+
     while(cbegin < cend)
     {
         uint32_t ch;

tests/simple.c

@@ -41,6 +41,8 @@ int main(int argc, char *argv[])
     caca_put_char(cv, 0, 0, 'x');
     TEST(caca_get_char(cv, 0, 0) != 'x');
 
+    caca_rotate_180(cv);
+
     caca_set_canvas_size(cv, 1, 1);
     TEST(caca_get_char(cv, 0, 0) != 'x');
     TEST(caca_get_char(cv, 0, 0) == ' ');