Bug: Fix incorrect CodeQL Fix - REBASE with PR 6024 (#819)

(cherry picked from commit f26f86d)

# Description

In commit
2998774
an unintentional code change in BmBoot BmExpandFileDevicePath was
introduced. The change intended to fix a CodeQL error but introduced a
failure with the boot managers ability to expand a "short" file device
path boot option.


- [X] Impacts functionality?
- **Functionality** - Does the change ultimately impact how firmware
functions?
- Examples: Add a new library, publish a new PPI, update an algorithm,
...
- [ ] 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

Tested on VM

## Integration Instructions

NA

MdeModulePkg/Library/UefiBootManagerLib/BmBoot.c

@@ -718,16 +718,21 @@ BmExpandFileDevicePath (
           ((MediaType == 2) && (BlockIo == NULL))
           )
       {
+        NextFullPath = AppendDevicePath (DevicePathFromHandle (Handles[Index]), FilePath);
+        if (NextFullPath == NULL) {
+          continue;
+        }
+
         if (GetNext) {
+          // this is the break/exit condition.  Occurs on first if FullPath input parameter was NULL
+          // or on the next loop after input parameter FullPath matches NextFullPath.
+          // NextFullPath will not be NULL so outer loop is broken too
           break;
         }
 
-        NextFullPath = AppendDevicePath (DevicePathFromHandle (Handles[Index]), FilePath);
-        if (NextFullPath != NULL) {
-          GetNext = (BOOLEAN)(CompareMem (NextFullPath, FullPath, GetDevicePathSize (NextFullPath)) == 0);
-          FreePool (NextFullPath);
-          NextFullPath = NULL;
-        }
+        GetNext = (BOOLEAN)(CompareMem (NextFullPath, FullPath, GetDevicePathSize (NextFullPath)) == 0);
+        FreePool (NextFullPath);
+        NextFullPath = NULL;
       }
     }