Require ruby-vips before downloading blob

This ensures that if `download_blob_to_tempfile` raises an error before
evaluating its block, `rescue ::Vips::Error` will not cause a
`NameError` due to `ruby-vips` not being loaded yet.

This also prevents the blob from being downloaded if `ruby-vips` is not
available to analyze it.

A similar change was made for `Analyzer::ImageAnalyzer::ImageMagick`
in #45420.

activestorage/lib/active_storage/analyzer/image_analyzer/vips.rb

@@ -10,9 +10,14 @@ module ActiveStorage
 
     private
       def read_image
-        download_blob_to_tempfile do |file|
+        begin
           require "ruby-vips"
+        rescue LoadError
+          logger.info "Skipping image analysis because the ruby-vips gem isn't installed"
+          return {}
+        end
 
+        download_blob_to_tempfile do |file|
           image = instrument("vips") do
             ::Vips::Image.new_from_file(file.path, access: :sequential)
           end
@@ -23,13 +28,10 @@ module ActiveStorage
             logger.info "Skipping image analysis because Vips doesn't support the file"
             {}
           end
+        rescue ::Vips::Error => error
+          logger.error "Skipping image analysis due to an Vips error: #{error.message}"
+          {}
         end
-      rescue LoadError
-        logger.info "Skipping image analysis because the ruby-vips gem isn't installed"
-        {}
-      rescue ::Vips::Error => error
-        logger.error "Skipping image analysis due to an Vips error: #{error.message}"
-        {}
       end
 
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