Fix multiple bugs in chat plugin integrations and Vault

[Smorki]

Description

This PR fixes four small but real bugs I noticed while reading through the codebase.

1. Chat_PermissionsEx — null check on wrong variable

Four methods (getGroupPrefix, setGroupPrefix, getGroupSuffix, setGroupSuffix) check if (group != null) where group is the String parameter (never null in practice) instead of pGroup, the resolved PermissionGroup (which CAN be null if the group name doesn't exist). This means when a non-existent group name is passed, the null check silently passes and the next line NPEs on pGroup.

Fix: Check pGroup != null instead of group != null.

2. Chat_OverPermissions — setGroupSuffix writes to "prefix" key

Copy-paste bug: setGroupSuffix calls setGroupInfoString(world, group, "prefix", suffix), overwriting the group's prefix with the suffix value instead of setting the suffix.

Fix: "prefix" → "suffix".

3. Vault.java — missing null check in findCustomData

findCustomData null-checks the RegisteredServiceProvider for Economy and Chat before calling .getProvider(), but does not null-check Permission. If no permission provider is registered (edge case, but possible), this would NPE.

Fix: Apply the same null-check pattern used for Economy and Chat, defaulting to "No Permission" when unavailable.

4. Vault.java — typo "Converson" → "Conversion"

Admin-facing typo in the /vault-convert command output.

Notes

• No public API changes.
• All fixes are behavior-preserving for the intended code path.
• The Chat_PermissionsEx and Chat_OverPermissions bugs affect users of those permission plugins when calling group-related methods.
• The Vault.java null-check brings consistency with the existing Economy/Chat handling pattern in the same method.

[Smorki]

can anyone review?