Player: explicitly check for false return of dataPacket()

fixes a phpstan error on l7
this won't ever actually be a problem, but this isn't obvious from the type system.

tests/phpstan/configs/l7-baseline.neon

@@ -45,11 +45,6 @@ parameters:
 			count: 1
 			path: ../../../src/pocketmine/Player.php
 
-		-
-			message: "#^Only booleans are allowed in an if condition, bool\\|int given\\.$#"
-			count: 1
-			path: ../../../src/pocketmine/Player.php
-
 		-
 			message: "#^Parameter \\#1 \\$haystack of function substr_count expects string, string\\|false given\\.$#"
 			count: 1