Two small tweaks on plot filename behavior: (1) "plot svg" without

a filename causes an error instead of generating a trash filename
or crashing, while (2) "plot pnm" with a filename that has the ".pnm"
extension does not add another ".pnm" extension to the end of it.

graphics/grTCairo1.c

@@ -355,6 +355,7 @@ void
 GrTCairoPlotSVG (char *filename, MagWindow *mw)
 {
     int screenw, screenh;
+    char *fileptr;
     cairo_surface_t *wind_surface;
     cairo_t *wind_context;
 
@@ -366,16 +367,28 @@ GrTCairoPlotSVG (char *filename, MagWindow *mw)
 	return;
     }
 
+    /* Add file extension ".svg" if the filename does not already have an
+     * extension.
+     */
+    fileptr = filename;
+    if (strchr(filename, '.') == NULL)
+    {
+	fileptr = mallocMagic(strlen(filename) + 5);
+	sprintf(fileptr, "%s.svg", filename);
+    }
+
     screenw = mw->w_screenArea.r_xtop - mw->w_screenArea.r_xbot;
     screenh = mw->w_screenArea.r_ytop - mw->w_screenArea.r_ybot;
 
     wind_surface = tcairodata->surface;
     wind_context = tcairodata->context;
-    tcairodata->surface = (cairo_surface_t *)cairo_svg_surface_create(filename,
+    tcairodata->surface = (cairo_surface_t *)cairo_svg_surface_create(fileptr,
 		(double)screenw, (double)screenh);
     cairo_svg_surface_restrict_to_version(tcairodata->surface,
 		CAIRO_SVG_VERSION_1_2);
 
+    if (fileptr != filename) freeMagic(fileptr);
+
     tcairodata->context = cairo_create(tcairodata->surface);
     WindRedisplay(mw);
     WindUpdate();

plot/plotCmd.c

@@ -269,9 +269,9 @@ CmdPlot(w, cmd)
 
 #if defined(HAVE_LIBCAIRO) && defined(MAGIC_WRAPPER)
 	case PLOTSVG:
-	    if (cmd->tx_argc > 3)
+	    if (cmd->tx_argc != 3)
 	    {
-		TxError("Too many arguments:\n    plot %s\n",
+		TxError("Wrong number of arguments:\n    plot %s\n",
 			cmdPlotOption[PLOTSVG]);
 		return;
 	    }

plot/plotPNM.c

@@ -755,6 +755,12 @@ PlotPNM(fileName, scx, layers, xMask, width)
 	    }
 	    fileName = tempFile;
 	}
+	else if (strchr(fileName, '.') == NULL)
+	{
+	    /* Add extention ".pnm" if the filename does not have an extension */
+	    sprintf(tempFile, "%s.pnm", fileName);
+	    fileName = tempFile;
+	}
 	rtl_args.outfile = PaOpen(fileName, "w", (char *)NULL, ".",
 		(char *)NULL, (char **)NULL);
 	if (rtl_args.outfile == NULL)
@@ -807,7 +813,9 @@ PlotPNM(fileName, scx, layers, xMask, width)
     {
 	/* open PNM file */
 
-	fp = PaOpen (fileName, "w", ".pnm", ".", NULL, NULL);
+	fp = PaOpen (fileName, "w",
+			(strchr(fileName, '.') == NULL) ? ".pnm" : NULL,
+			".", NULL, NULL);
 	if (fp == NULL)
 	{
 	    TxError ("Could not open file `%s' for writing\n", fileName);