[9.18] Fix scan-build issue: initialized value never read

Merged Matthijs Mekking requested to merge 3965-source-never-read-master.c-v9_18 into bind-9.18

Backport of MR !7725 (merged)

Value stored to 'source' during its initialization is never read.

(cherry picked from commit 4c332774)

Closes #3965 (closed)

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