libutil: Fix Pos::getSourcePath

Previous implementation didn't actually check if
std::get_if returned a nullptr:

std::optional<SourcePath> getSourcePath() const {
    return *std::get_if<SourcePath>(&origin);
}

Author: xokdvium

src/libutil/position.cc

@@ -66,6 +66,13 @@ std::optional<std::string> Pos::getSource() const
     }, origin);
 }
 
+std::optional<SourcePath> Pos::getSourcePath() const
+{
+    if (auto * path = std::get_if<SourcePath>(&origin))
+        return *path;
+    return std::nullopt;
+}
+
 void Pos::print(std::ostream & out, bool showOrigin) const
 {
     if (showOrigin) {

src/libutil/position.hh

@@ -70,9 +70,7 @@ struct Pos
     /**
      * Get the SourcePath, if the source was loaded from a file.
      */
-    std::optional<SourcePath> getSourcePath() const {
-        return *std::get_if<SourcePath>(&origin);
-    }
+    std::optional<SourcePath> getSourcePath() const;
 
     struct LinesIterator {
         using difference_type = size_t;