perf: optimize getting random quote

building new vec of quotes for it to be selected one at random from is
overhead, building new vec is required only in case of filtering, for
example, by character

src/main.rs

@@ -36,14 +36,20 @@ fn main() -> Result<(), &'static str> {
 }
 
 fn get_random_quote(char: Option<String>) -> Result<&'static Quote, &'static str> {
-	let quotes: Vec<&Quote> = match char {
-		None => QUOTES.iter().collect(),
-		Some(char) => QUOTES.iter()
-			.filter(|quote| quote.char.to_str().to_lowercase().contains(&char.to_lowercase()))
-			.collect()
-	};
-	if quotes.len() == 0 { return Err("Character or her quote not found.") }
 	let mut rng = thread_rng();
-	let random_quote_index: usize = rng.gen_range(0..quotes.len());
-	Ok(quotes[random_quote_index])
+	match char {
+		None => {
+			let random_quote_index: usize = rng.gen_range(0..QUOTES.len());
+			Ok(&QUOTES[random_quote_index])
+		}
+		Some(char) => {
+			let char_lowercase: String = char.to_lowercase();
+			let quotes: Vec<&Quote> = QUOTES.iter()
+				.filter(|quote| quote.char.to_str().to_lowercase().contains(&char_lowercase))
+				.collect();
+			if quotes.len() == 0 { return Err("Character's quote not found.") }
+			let random_quote_index: usize = rng.gen_range(0..quotes.len());
+			Ok(quotes[random_quote_index])
+		}
+	}
 }