Typogrify alt attributes in images when a DOM can be parsed

Fixes standardebooks#724

se/commands/typogrify.py

@@ -57,7 +57,12 @@ def typogrify(plain_output: bool) -> int:
 
 								processed_xhtml = dom.to_string()
 						else:
-							processed_xhtml = se.typography.typogrify(xhtml, args.quotes)
+							for node in dom.xpath("/html/body//img[@alt]"):
+								node.set_attr("alt", se.typography.typogrify(node.get_attr("alt"), args.quotes))
+
+							processed_xhtml = dom.to_string()
+							# Word joiners and nbsp don't belong in alt but that is handled by typogrify itself
+							processed_xhtml = se.typography.typogrify(processed_xhtml, args.quotes)
 
 						# Tweak: Word joiners and nbsp don't go in the ToC
 						if dom.xpath("/html/body//nav[contains(@epub:type, 'toc')]"):

tests/draft_commands/typogrify/test-1/golden/typogrify.xhtml

@@ -10,6 +10,7 @@
 			<h2 epub:type="title">A Dreary Story</h2>
 			<!-- Straight quotes converted to curly quotes -->
 			<p>content of “chapter 1”</p>
+			<img alt="“Typography’s great …”—you can quote me on that."/>
 			<!-- Appropriate quotes for ’tis or equivalent -->
 			<ul>
 				<li>’tis</li>

tests/draft_commands/typogrify/test-1/in/typogrify.xhtml

@@ -10,6 +10,7 @@
 			<h2 epub:type="title">A Dreary Story</h2>
 			<!-- Straight quotes converted to curly quotes -->
 			<p>content of "chapter 1"</p>
+			<img alt="&quot;Typography's great...&quot; -- you can quote me on that."/>
 			<!-- Appropriate quotes for ’tis or equivalent -->
 			<ul>
 				<li>'tis</li>