Fix regex mistake in CB NBT int deserialization (#4146)

The existing regex is too open and allows for the absence of any actual
number data, detecting an NBT entry of just the letter "i" in upper or
lower case. This causes a single-character NBT entry to be processed as
an integer ending in "i", passing an empty String to to Integer.parseInt,
triggering an exception in loading the item.

This commit forces numbers to be present prior to the ending "i"
letter.

Spigot-Server-Patches/0552-Fix-regex-mistake-in-CB-NBT-int-deserialization.patch

@@ -0,0 +1,27 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: mbax <matt@phozop.net>
+Date: Mon, 17 Aug 2020 12:17:37 -0400
+Subject: [PATCH] Fix regex mistake in CB NBT int deserialization
+
+The existing regex is too open and allows for the absence of any actual
+number data, detecting an NBT entry of just the letter "i" in upper or
+lower case. This causes a single-character NBT entry to be processed as
+an integer ending in "i", passing an empty String to to Integer.parseInt,
+triggering an exception in loading the item.
+
+This commit forces numbers to be present prior to the ending "i"
+letter.
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/util/CraftNBTTagConfigSerializer.java b/src/main/java/org/bukkit/craftbukkit/util/CraftNBTTagConfigSerializer.java
+index b17faa25e6db28e8538cc21d7a651e4acdf0c580..373dfe726c5ec4f3011f77e08d3e0850ffecf5ed 100644
+--- a/src/main/java/org/bukkit/craftbukkit/util/CraftNBTTagConfigSerializer.java
++++ b/src/main/java/org/bukkit/craftbukkit/util/CraftNBTTagConfigSerializer.java
+@@ -19,7 +19,7 @@ import net.minecraft.server.NBTTagString;
+ public class CraftNBTTagConfigSerializer {
+ 
+     private static final Pattern ARRAY = Pattern.compile("^\\[.*]");
+-    private static final Pattern INTEGER = Pattern.compile("[-+]?(?:0|[1-9][0-9]*)?i", Pattern.CASE_INSENSITIVE);
++    private static final Pattern INTEGER = Pattern.compile("[-+]?(?:0|[1-9][0-9]*)i", Pattern.CASE_INSENSITIVE); // Paper - fix regex
+     private static final Pattern DOUBLE = Pattern.compile("[-+]?(?:[0-9]+[.]?|[0-9]*[.][0-9]+)(?:e[-+]?[0-9]+)?d", Pattern.CASE_INSENSITIVE);
+     private static final MojangsonParser MOJANGSON_PARSER = new MojangsonParser(new StringReader(""));
+