Fix: String parameter not set when determining width of smallmap contour labels. (#13145)

src/smallmap_gui.cpp

@@ -1559,6 +1559,7 @@ public:
 					}
 					height++;
 					str = tbl->legend;
+					if (i == SMT_CONTOUR) SetDParam(0, tbl->height * TILE_HEIGHT_STEP);
 				}
 				min_width = std::max(GetStringBoundingBox(str).width, min_width);
 			}