Fix string.drop_end to handle zero gracefully

Author: JosephTLyons

src/gleam/string.gleam

@@ -248,7 +248,7 @@ pub fn drop_start(from string: String, up_to num_graphemes: Int) -> String {
 /// ```
 ///
 pub fn drop_end(from string: String, up_to num_graphemes: Int) -> String {
-  case num_graphemes < 0 {
+  case num_graphemes <= 0 {
     True -> string
     False -> slice(string, 0, length(string) - num_graphemes)
   }

test/gleam/string_test.gleam

@@ -356,6 +356,8 @@ pub fn drop_start_test() {
   assert string.drop_start("gleam", up_to: 6) == ""
 
   assert string.drop_start("gleam", up_to: -2) == "gleam"
+
+  assert string.drop_start("gleam", up_to: 0) == "gleam"
 }
 
 pub fn drop_start_3499_test() {
@@ -369,6 +371,8 @@ pub fn drop_end_test() {
   assert string.drop_end("gleam", up_to: 5) == ""
 
   assert string.drop_end("gleam", up_to: -2) == "gleam"
+
+  assert string.drop_end("gleam", up_to: 0) == "gleam"
 }
 
 pub fn pad_start_test() {