Fix possible integer overflow in multiplication

[EnricoMi]

CodeQL identified a few integer multiplications that might overflow before cast to a larger type:

Multiplication result may overflow 'int' before it is converted to 'int64_t'.

This rule finds code that converts the result of an integer multiplication to a larger type.
Since the conversion applies after the multiplication, arithmetic overflow may still occur.

See CWE-190 CWE-192 CWE-197 CWE-681.

Fixes:
https://github.com/horovod/horovod/security/code-scanning/3
https://github.com/horovod/horovod/security/code-scanning/4
https://github.com/horovod/horovod/security/code-scanning/5
https://github.com/horovod/horovod/security/code-scanning/6
https://github.com/horovod/horovod/security/code-scanning/7
https://github.com/horovod/horovod/security/code-scanning/8

See: https://github.com/horovod/horovod/runs/4816240959

[github-actions]

Unit Test Results

     802 files  ±0       802 suites  ±0   8h 58m 39s ⏱️ + 13m 10s
     717 tests ±0       672 ✔️ ±0       45 💤 ±0  0 ❌ ±0 
17 324 runs  ±0  12 238 ✔️ ±0  5 086 💤 ±0  0 ❌ ±0 

Results for commit 3f91c86. ± Comparison against base commit 0b1a4a6.

[github-actions]

Unit Test Results (with flaky tests)

     890 files   -   56       890 suites   - 56   9h 25m 26s ⏱️ - 10m 51s
     717 tests ±    0       671 ✔️ +    3       45 💤 ±    0  1 ❌  - 3 
19 430 runs   - 938  13 551 ✔️  - 672  5 878 💤  - 263  1 ❌  - 3 

For more details on these failures, see this check.

Results for commit 3f91c86. ± Comparison against base commit 0b1a4a6.