fmt: fix optional_len or use_nul_termination being used by both array and elems

```odin
My_Struct :: struct {
	names:      [^]string `fmt:"v,name_count"`,
	name_count: int,
}

main :: proc() {
	name := "hello?"
	foo := My_Struct {
		names = &name,
		name_count = 1,
	}
	fmt.println(foo)
}
```

Before: `My_Struct{names = ["h"], name_count = 1}`
After:  `My_Struct{names = ["hello?"], name_count = 1}`

core/fmt/fmt.odin

@@ -2751,9 +2751,11 @@ fmt_value :: proc(fi: ^Info, v: any, verb: rune) {
 			elem := runtime.type_info_base(info.elem)
 			if elem != nil {
 				if n, ok := fi.optional_len.?; ok {
+					fi.optional_len = nil
 					fmt_array(fi, ptr, n, elem.size, elem, verb)
 					return
 				} else if fi.use_nul_termination {
+					fi.use_nul_termination = false
 					fmt_array_nul_terminated(fi, ptr, -1, elem.size, elem, verb)
 					return
 				}
@@ -2855,8 +2857,10 @@ fmt_value :: proc(fi: ^Info, v: any, verb: rune) {
 		n := info.count
 		ptr := v.data
 		if ol, ok := fi.optional_len.?; ok {
+			fi.optional_len = nil
 			n = min(n, ol)
 		} else if fi.use_nul_termination {
+			fi.use_nul_termination = false
 			fmt_array_nul_terminated(fi, ptr, n, info.elem_size, info.elem, verb)
 			return
 		}
@@ -2867,8 +2871,10 @@ fmt_value :: proc(fi: ^Info, v: any, verb: rune) {
 		n := slice.len
 		ptr := slice.data
 		if ol, ok := fi.optional_len.?; ok {
+			fi.optional_len = nil
 			n = min(n, ol)
 		} else if fi.use_nul_termination {
+			fi.use_nul_termination = false
 			fmt_array_nul_terminated(fi, ptr, n, info.elem_size, info.elem, verb)
 			return
 		}
@@ -2879,8 +2885,10 @@ fmt_value :: proc(fi: ^Info, v: any, verb: rune) {
 		n := array.len
 		ptr := array.data
 		if ol, ok := fi.optional_len.?; ok {
+			fi.optional_len = nil
 			n = min(n, ol)
 		} else if fi.use_nul_termination {
+			fi.use_nul_termination = false
 			fmt_array_nul_terminated(fi, ptr, n, info.elem_size, info.elem, verb)
 			return
 		}