String: is_empty + proper initialization

libluna/include/luna/String.h

@@ -30,6 +30,11 @@ class String
         return m_length;
     }
 
+    bool is_empty() const
+    {
+        return m_length == 0;
+    }
+
     const char& operator[](usize) const;
 
   private:

libluna/src/String.cpp

@@ -5,6 +5,7 @@
 String::String()
 {
     m_inline = true;
+    m_length = 0;
     memset(m_inline_storage, 0, sizeof(m_inline_storage));
 }
 
@@ -22,14 +23,15 @@ String::String(String&& other)
 
 String::String(char* c_str)
 {
+    check(c_str);
     m_string = c_str;
     m_inline = false;
-
-    if (m_string) { m_length = strlen(m_string); }
+    m_length = strlen(m_string);
 }
 
 String::String(char* c_str, usize length)
 {
+    check(c_str);
     m_string = c_str;
     m_inline = false;
     m_length = length;
@@ -61,10 +63,12 @@ const char& String::operator[](usize index) const
 
 Result<String> String::from_string_literal(const char* str)
 {
-    if (strlen(str) < sizeof(m_inline_storage))
+    usize len = strlen(str);
+    if (len < sizeof(m_inline_storage))
     {
         String result;
         result.m_inline = true;
+        result.m_length = len;
         strncpy(result.m_inline_storage, str, sizeof(m_inline_storage));
         return result;
     }