Qual: Better hint for index value for phan (#28712)

# Qual: Better hint for index value for phan.

($i - 1) must be >= 0, so update test from $i>0 to $i>=1 .
This helps static analysis.

htdocs/core/lib/json.lib.php

@@ -267,7 +267,7 @@ function dol_json_decode($json, $assoc = false)
 		} else {
 			$out .= $json[$i];
 		}
-		if ($i > 0 && $json[$i] == '"' && $json[($i - 1)] != "\\") {
+		if ($i >= 1 && $json[$i] == '"' && $json[$i - 1] != "\\") {
 			$comment = !$comment;
 		}
 	}