fix rendering url of highlight note

app/src/main/java/com/vitorpamplona/amethyst/model/LocalCache.kt

@@ -51,6 +51,7 @@ object LocalCache {
     }
 
     fun getUserIfExists(key: String): User? {
+        if (key.isEmpty()) return null
         return users[key]
     }
 
@@ -108,6 +109,7 @@ object LocalCache {
     }
 
     private fun isValidHexNpub(key: String): Boolean {
+        if (key.isBlank()) return false
         if (key.contains(":")) return false
 
         return HexValidator.isHex(key)

app/src/main/java/com/vitorpamplona/amethyst/ui/note/NoteCompose.kt

@@ -2081,9 +2081,7 @@ fun DisplayHighlight(
         nav
     )
 
-    authorHex?.let {
-        DisplayQuoteAuthor(authorHex, url, nav)
-    }
+    DisplayQuoteAuthor(authorHex ?: "", url, nav)
 }
 
 @Composable
@@ -2105,7 +2103,7 @@ private fun DisplayQuoteAuthor(
         }
     }
 
-    Row() {
+    Row {
         userBase?.let { userBase ->
             LoadAndDisplayUser(userBase, nav)
         }