templates: Fix front matter closing fence search

This makes it choose first matching closing fence instead of last one,
which could appear in document body.

modules/caddyhttp/templates/frontmatter.go

@@ -56,6 +56,7 @@ func extractFrontMatter(input string) (map[string]interface{}, string, error) {
 		if index >= 0 {
 			fmEndFenceStart = index
 			fmEndFence = fence
+			break
 		}
 	}
 	if fmEndFenceStart < 0 {

modules/caddyhttp/templates/tplcontext_test.go

@@ -316,6 +316,17 @@ title: Welcome
 			expect: `Welcome`,
 			body:   "\n### Test",
 		},
+		{
+			// yaml with non-fence '...' line after closing fence (i.e. first matching closing fence should be used)
+			input: `---
+title: Welcome
+---
+### Test
+...
+yeah`,
+			expect: `Welcome`,
+			body:   "\n### Test\n...\nyeah",
+		},
 		{
 			// toml
 			input: `+++