FIX: Allow SVG uploads if dimensions are a fraction of a unit (#13409)

* FIX: Allow SVG uploads if dimensions are a fraction of a unit

`UploadCreator` counts the number of pixels in an file to determine if it is valid. `pixels` is calculated by multiplying the width and height of the image, as determined by FastImage.

SVG files can have their width/height expressed in a variety of different units of measurement. For example, ‘px’, ‘in’, ‘cm’, ‘mm’, ‘pt’, ‘pc’, etc are all valid within SVG files. If an image has a width of `0.5in`, FastImage may interpret this as being a width of `0`, meaning it will report the `size` as being `0`.

However, we don’t need to concern ourselves with the number of ‘pixels’ in a SVG files, as that is irrelevant for this file format, so we can skip over the check for `pixels == 0` when processing this file type.

* DEV: Speed up getting SVG dimensions

The `-ping` flag prevents the entire image from being rasterized before a result is returned. See:

https://imagemagick.org/script/command-line-options.php#ping

spec/lib/upload_creator_spec.rb

@@ -570,17 +570,50 @@ RSpec.describe UploadCreator do
     end
   end
 
-  describe "svg sizing" do
-    let(:svg_filename) { "pencil.svg" }
-    let(:svg_file) { file_from_fixtures(svg_filename) }
+  describe "svg sizes expressed in units other than pixels" do
+    let(:tiny_svg_filename) { "tiny.svg" }
+    let(:tiny_svg_file) { file_from_fixtures(tiny_svg_filename) }
 
-    it "should handle units in width and height" do
-      upload = UploadCreator.new(svg_file, svg_filename,
+    let(:massive_svg_filename) { "massive.svg" }
+    let(:massive_svg_file) { file_from_fixtures(massive_svg_filename) }
+
+    let(:zero_sized_svg_filename) { "zero_sized.svg" }
+    let(:zero_sized_svg_file) { file_from_fixtures(zero_sized_svg_filename) }
+
+    it "should be viewable when a dimension is a fraction of a unit" do
+      upload = UploadCreator.new(tiny_svg_file, tiny_svg_filename,
         force_optimize: true,
       ).create_for(user.id)
 
-      expect(upload.width).to be > 100
-      expect(upload.height).to be > 100
+      expect(upload.width).to be > 50
+      expect(upload.height).to be > 50
+
+      expect(upload.thumbnail_width).to be <= SiteSetting.max_image_width
+      expect(upload.thumbnail_height).to be <= SiteSetting.max_image_height
+    end
+
+    it "should not be larger than the maximum thumbnail size" do
+      upload = UploadCreator.new(massive_svg_file, massive_svg_filename,
+        force_optimize: true,
+      ).create_for(user.id)
+
+      expect(upload.width).to be > 50
+      expect(upload.height).to be > 50
+
+      expect(upload.thumbnail_width).to be <= SiteSetting.max_image_width
+      expect(upload.thumbnail_height).to be <= SiteSetting.max_image_height
+    end
+
+    it "should handle zero dimension files" do
+      upload = UploadCreator.new(zero_sized_svg_file, zero_sized_svg_filename,
+        force_optimize: true,
+      ).create_for(user.id)
+
+      expect(upload.width).to be > 50
+      expect(upload.height).to be > 50
+
+      expect(upload.thumbnail_width).to be <= SiteSetting.max_image_width
+      expect(upload.thumbnail_height).to be <= SiteSetting.max_image_height
     end
   end