Image is not cropped by `gmt end` via the API

The API can be used to create an image file with exactly the same instructions as a script. However, with or without the A option on the ``gmt begin`` line, the figure is not cropped when ``gmt end show`` is called.

Take this simple script:

gmt begin toto_script jpg

gmt basemap -BWESN -Bxa30mg30m -Bya20mg20m -JM7.27/42.27/16.25c -R5.5/41.425/9.0/43.1r

gmt end show

resulting in this image:


The same instructions via the API:

int main () {

void *API;


/* Initialize the GMT session */

if ((API = GMT_Create_Session ("GMT_plot", 2, 0, NULL)) == NULL)

   return EXIT_FAILURE;

GMT_Call_Module(API, "begin", GMT_MODULE_CMD, "toto_api jpg");

GMT_Call_Module(API, "basemap", GMT_MODULE_CMD, "-BWESN -Bxa30mg30m -Bya20mg20m -JM7.27/42.27/16.25c -R5.5/41.425/9.0/43.1r");

GMT_Call_Module(API, "end", GMT_MODULE_CMD, "show");

/* Destroy session */

if (GMT_Destroy_Session (API)) 

  return EXIT_FAILURE;

}

produce a different image, not cropped:


Running ``gmt end show -Vd`` reveals the difference between script and API processing:

From script:
` end [DEBUG]: psconvert: '/home/sarzeaud/.gmt/sessions/gmt_session.14414/gmt_0.ps-' -Tj -Ftoto -A`
From C program (-A option is missing):
` end [DEBUG]: psconvert: '/home/sarzeaud/.gmt/sessions/gmt_session.14414/gmt_0.ps-' -Tj -Ftoto`

The result is the same whether or not we use the A option on the ``gmt begin`` line.

**System information**

* Operating system: Debian stretch
* GMT version (`gmt --version`): 6.2.0_d266c30_2020.11.25