Until solved, disallow subplot tags with Latex (#8018)

This PR implements a solution that skips any Latex tags for a panel rather than resulting in a ghostscript crash and no plot.  SHould we solbe the issue later then we can work on the branch that tries to support it.

Author: PaulWessel

src/gmt_plot.c

@@ -9250,6 +9250,13 @@ struct PSL_CTRL *gmt_plotinit (struct GMT_CTRL *GMT, struct GMT_OPTION *options)
 		/* Place the panel tag, once per panel (if requested), then update the gmt.panel file to say we have been there */
 		if (strcmp (P->tag, "-")) {	/* Place the panel tag */
 			int form, refpoint, justify;
+
+			if (gmt_text_is_latex (GMT, P->tag)) {	/* LaTeX commands, i.e., "....@[LaTeX...@[ ..." or  "....<math>LaTeX...</math> ..." not supported in tags */
+				/* See branch latex-in-subplot-tags. We get gs error when I tried to implement the standard solution inside the PSL_completion function.
+				 * More work is needed to learn what goes wrong, probably by asking on the ghostscript help/support line. */
+				GMT_Report (GMT->parent, GMT_MSG_WARNING, "Latex expressions are not (yet) supported as subplot panel tags - use text instead\n");
+				goto no_latex_tags;
+			}
 			refpoint = gmt_just_decode (GMT, P->refpoint, PSL_NO_DEF);	/* Convert XX refpoint code to PSL number */
 			gmtlib_refpoint_to_panel_xy (GMT, refpoint, P, &plot_x, &plot_y);	/* Convert just code to panel location */
 			/* Undo any offsets above that was required to center the plot on the subplot panel */
@@ -9296,6 +9303,7 @@ struct PSL_CTRL *gmt_plotinit (struct GMT_CTRL *GMT, struct GMT_OPTION *options)
 			PSL_comment (PSL, "End of panel tag for panel (%d,%d)\n", P->row, P->col);
 			PSL_command (PSL, "U\n}!\n");
 		}
+no_latex_tags:
 		/* Store first = 0 since we are done with -B and the optional tag */
 		if (gmt_set_current_panel (GMT->parent, GMT->current.ps.figure, P->row, P->col, P->gap, P->tag, 0))
 			return NULL;	/* Should never happen */