uefi: Revise env functions to use panicking function calls

Co-authored-by: Philipp Schuster <phip1611@gmail.com>

Author: RenTrieu

uefi/src/proto/shell/mod.rs

@@ -63,9 +63,9 @@ impl Shell {
             while null_count <= 1 {
                 if (*(cur_env_ptr.add(i))) == Char16::from_u16_unchecked(0).into() {
                     if cur_len > 0 {
-                        env_vec.push(CStr16::from_char16_with_nul_unchecked(
+                        env_vec.push(CStr16::from_char16_with_nul(
                             &(*ptr::slice_from_raw_parts(cur_start.cast(), cur_len + 1)),
-                        ));
+                        ).unwrap());
                     }
                     cur_len = 0;
                     null_count += 1;
@@ -88,7 +88,7 @@ impl Shell {
     ///
     /// * `name` - The environment variable for which to set the value
     /// * `value` - The new value of the environment variable
-    /// * `volatile` - Indicates whether or not the variable is volatile or
+    /// * `volatile` - Indicates whether the variable is volatile or
     ///   not
     ///
     /// # Returns