Fix JNI crash when jBytes is null in SafeConvertToStdString

[kevingpqi123]

Problem

When calling SafeConvertToStdString, if String.getBytes() returns null (due to OOM or other JNI exceptions), the subsequent GetArrayLength(jBytes) call will crash with:

JNI DETECTED ERROR IN APPLICATION: java_array == null

Related issue: #3045

Solution

Add null check and exception handling for jBytes before calling GetArrayLength:

if (jBytes == nullptr || env->ExceptionCheck()) {
  env->ExceptionClear();
  return "";
}

Changes

• Added null check for jBytes after CallObjectMethod
• Added ExceptionCheck() to detect pending JNI exceptions
• Call ExceptionClear() to clear any pending exception before returning

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.11%. Comparing base (187bd07) to head (bf16908).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3254   +/-   ##
=======================================
  Coverage   77.10%   77.11%           
=======================================
  Files         415      415           
  Lines       22040    22040           
  Branches     6307     6307           
=======================================
+ Hits        16995    16997    +2     
+ Misses       3818     3817    -1     
+ Partials     1227     1226    -1     

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