Zero instead of NULL used in MD_ManageDwellTable() in md_app.c

[myc-yang]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I performed a cursory search to see if the bug report is relevant, not redundant, nor in conflict with other tickets.

Describe the bug
In MD_ManageDwellTable() in md_app.c, MD_LoadTablePtr is initialized to zero instead of NULL.

To Reproduce
Steps to reproduce the behavior:

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4. See error

Expected behavior
According to MISRA C:2012 11.9: The macro NULL shall be the only permitted form of integer null pointer constant.

Code snips
If applicable, add references to the software.

System observed on:

• Hardware
• OS: [e.g. Linux 4.4]
• Versions [e.g. cFE 6.6, OSAL 4.2, PSP 1.3 for mcp750, any related apps]

Additional context
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Reporter Info
Michael Yang / NASA GSFC