fix: set link for first uncovered line

A link tag existed that should move to the first uncovered line in
source view, but it never contained a proper working URL.

Also, the link won't be generated anymore if there aren't any uncovered
lines in the file.

src/templates.rs

@@ -68,6 +68,11 @@ pub struct Source<'a> {
 }
 
 impl<'a> Source<'a> {
+    fn get_first(&self) -> Option<usize> {
+        (1..=self.lines.len())
+            .find(|line| matches!(self.get_coverage(line), Coverage::Uncovered(_)))
+    }
+
     fn get_coverage(&self, index: &usize) -> Coverage {
         self.info
             .covered

templates/source.html

@@ -36,7 +36,11 @@
       <tr>
         <th>Line</th>
         <th>Count</th>
-        <th>Source (<a>jump to first uncovered line</a>)</th>
+        <th>Source
+        {%- if let Some(line) = self.get_first() %}
+          (<a href="#L{{line}}">jump to first uncovered line</a>)
+        {% endif -%}
+        </th>
       </tr>
     </thead>
     <tbody class="syntect-code">