add zero address checks in constructor

[trmid]

No description provided.

[linear]

GEN-496 C4 Bot Results: [LOW-14] Missing zero address check in constructor

https://github.com/code-423n4/2023-08-pooltogether/blob/main/bot-report.md#low-14-missing-zero-address-check-in-constructor

[github-actions]

LCOV of commit cb19885 during 100% Test Coverage #24

Summary coverage rate:
  lines......: 100.0% (51 of 51 lines)
  functions..: 100.0% (11 of 11 functions)
  branches...: no data found

Files changed coverage rate:
                             |Lines       |Functions  |Branches    
  Filename                   |Rate     Num|Rate    Num|Rate     Num
  =================================================================
  src/VaultBooster.sol       | 100%     48| 100%    10|    -      0

[github-actions]

LCOV of commit 820a55b during 100% Test Coverage #36

Summary coverage rate:
  lines......: 100.0% (57 of 57 lines)
  functions..: 100.0% (11 of 11 functions)
  branches...: no data found

Files changed coverage rate:
                             |Lines       |Functions  |Branches    
  Filename                   |Rate     Num|Rate    Num|Rate     Num
  =================================================================
  src/VaultBooster.sol       | 100%     54| 100%    10|    -      0