Fix comparison against nil for cstring

core/strings.odin

@@ -1,4 +1,5 @@
 import "core:mem.odin"
+import "core:raw.odin"
 
 new_string :: proc(s: string) -> string {
 	c := make([]byte, len(s)+1);
@@ -19,6 +20,10 @@ to_odin_string :: proc(str: cstring) -> string {
 	return string(str);
 }
 
+string_from_ptr :: proc(ptr: ^byte, len: int) -> string {
+	return transmute(string)raw.String{ptr, len};
+}
+
 contains_rune :: proc(s: string, r: rune) -> int {
 	for c, offset in s {
 		if c == r do return offset;