Make some casts in Agg renderer explicit

The Agg API uses `double`s here, but the array sizes are
`pybind11::ssize_t`, which are technically bigger (in some ways), and
cause a warning on MSVC. We don't accept a backing surface larger than
~2^16, so there's no worry about these overflowing.

Author: QuLogic

src/_backend_agg.h

@@ -350,7 +350,8 @@ RendererAgg::_draw_path(path_t &path, bool has_clippath, const facepair_t &face,
         agg::trans_affine hatch_trans;
         hatch_trans *= agg::trans_affine_scaling(1.0, -1.0);
         hatch_trans *= agg::trans_affine_translation(0.0, 1.0);
-        hatch_trans *= agg::trans_affine_scaling(hatch_size, hatch_size);
+        hatch_trans *= agg::trans_affine_scaling(static_cast<double>(hatch_size),
+                                                 static_cast<double>(hatch_size));
         hatch_path_trans_t hatch_path_trans(hatch_path, hatch_trans);
         hatch_path_curve_t hatch_path_curve(hatch_path_trans);
         hatch_path_stroke_t hatch_path_stroke(hatch_path_curve);
@@ -739,16 +740,19 @@ inline void RendererAgg::draw_text_image(GCAgg &gc, ImageArray &image, int x, in
 
         set_clipbox(gc.cliprect, theRasterizer);
 
+        auto image_height = static_cast<double>(image.shape(0)),
+             image_width = static_cast<double>(image.shape(1));
+
         agg::trans_affine mtx;
-        mtx *= agg::trans_affine_translation(0, -image.shape(0));
+        mtx *= agg::trans_affine_translation(0, -image_height);
         mtx *= agg::trans_affine_rotation(-angle * (agg::pi / 180.0));
         mtx *= agg::trans_affine_translation(x, y);
 
         agg::path_storage rect;
         rect.move_to(0, 0);
-        rect.line_to(image.shape(1), 0);
-        rect.line_to(image.shape(1), image.shape(0));
-        rect.line_to(0, image.shape(0));
+        rect.line_to(image_width, 0);
+        rect.line_to(image_width, image_height);
+        rect.line_to(0, image_height);
         rect.line_to(0, 0);
         agg::conv_transform<agg::path_storage> rect2(rect, mtx);
 
@@ -842,12 +846,15 @@ inline void RendererAgg::draw_image(GCAgg &gc,
         agg::trans_affine mtx;
         agg::path_storage rect;
 
-        mtx *= agg::trans_affine_translation((int)x, (int)(height - (y + image.shape(0))));
+        auto image_height = static_cast<double>(image.shape(0)),
+             image_width = static_cast<double>(image.shape(1));
+
+        mtx *= agg::trans_affine_translation((int)x, (int)(height - (y + image_height)));
 
         rect.move_to(0, 0);
-        rect.line_to(image.shape(1), 0);
-        rect.line_to(image.shape(1), image.shape(0));
-        rect.line_to(0, image.shape(0));
+        rect.line_to(image_width, 0);
+        rect.line_to(image_width, image_height);
+        rect.line_to(0, image_height);
         rect.line_to(0, 0);
 
         agg::conv_transform<agg::path_storage> rect2(rect, mtx);