Fixing uninitialized variable build error (#406)

## Description


267e27f
change introduced a build error on certain platforms, due to a local
variable being used uninitialized. This change will set the variable to
0 before usage.

- [ ] Impacts functionality?
- **Functionality** - Does the change ultimately impact how firmware
functions?
- Examples: Add a new library, publish a new PPI, update an algorithm,
...
- [x] Impacts security?
- **Security** - Does the change have a direct security impact on an
application,
    flow, or firmware?
  - Examples: Crypto algorithm change, buffer overflow fix, parameter
    validation improvement, ...
- [ ] Breaking change?
- **Breaking change** - Will anyone consuming this change experience a
break
    in build or boot behavior?
- Examples: Add a new library class, move a module to a different repo,
call
    a function in a new library class in a pre-existing module, ...
- [ ] Includes tests?
  - **Tests** - Does the change include any explicit test code?
  - Examples: Unit tests, integration tests, robot tests, ...
- [ ] Includes documentation?
- **Documentation** - Does the change contain explicit documentation
additions
    outside direct code modifications (and comments)?
- Examples: Update readme file, add feature readme file, link to
documentation
    on an a separate Web page, ...

## How This Was Tested

This change is tested with LineParserTestApp on QEMU Q35 platform.

## Integration Instructions

N/A

AdvLoggerPkg/Library/AdvancedLoggerAccessLib/AdvancedLoggerAccessLib.c

@@ -314,6 +314,7 @@ AdvancedLoggerAccessLibGetNextFormattedLine (
   // GetNextLine.
 
   // In case this is a restart of the same Message, initialize the time stamp and prefix.
+  PhaseStringLen = 0;
   if (LineEntry->BlockEntry.Message != NULL) {
     FormatTimeStamp (TimeStampString, sizeof (TimeStampString), LineEntry->BlockEntry.TimeStamp);
     CopyMem (LineBuffer, TimeStampString, sizeof (TimeStampString) - sizeof (CHAR8));