dissect-image: fix path building for non-raw images

If the passed in image path didn't end with .raw, we'd return an empty
string + suffix instead of the intended image + suffix path.

Follow-up for 89e62e0bd3.

src/shared/dissect-image.c

@@ -3728,7 +3728,7 @@ static char *build_auxiliary_path(const char *image, const char *suffix) {
 
         e = endswith(image, ".raw");
         if (!e)
-                return strjoin(e, suffix);
+                return strjoin(image, suffix);
 
         n = new(char, e - image + strlen(suffix) + 1);
         if (!n)