zig fmt: Fix rendering of arrays with single row

rowSize used to return null if all the elements were placed on the same
line as the right brace, making the rendering logic skip the whole set
of elements.

Given the usage of rowSize let's just drop the null and always return
the number of elements.

Fixes #8423

lib/std/zig/parser_test.zig

@@ -1812,6 +1812,8 @@ test "zig fmt: array literal veritical column alignment" {
         \\    4,5,600,7,
         \\           80,
         \\    9, 10, 11, 0, 13, 14, 15};
+        \\const a = [12]u8{
+        \\    31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
         \\
     ,
         \\const a = []u8{
@@ -1825,6 +1827,9 @@ test "zig fmt: array literal veritical column alignment" {
         \\    9,  10, 11,  0, 13,
         \\    14, 15,
         \\};
+        \\const a = [12]u8{
+        \\    31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31,
+        \\};
         \\
     );
 }