Fix the NPE issue in provisioner resource/datasource

[ramya-bangera]

1. What this PR does / why we need it: Added the fix to return without trying to parse the nil response in case of any error.

2. Which issue(s) this PR fixes Internal Jira

3. Additional information

4. Special notes for your reviewer

   

<testsuite name="github.com/vmware/terraform-provider-tanzu-mission-control/internal/resources/provisioner" tests="2" failures="0" errors="0" id="230" hostname="sc2-10-187-102-46.nimbus.eng.vmware.com" time="45.050" timestamp="2024-01-19T07:26:16Z">
        <properties>
            <property name="coverage.statements.pct" value="62.80"></property>
        </properties>
        <testcase name="TestAcceptanceForProvisionerDataSource" classname="github.com/vmware/terraform-provider-tanzu-mission-control/internal/resources/provisioner" time="15.960">
            <system-out><![CDATA[    provisioner_data_source_test.go:43: provisioner datasource acceptance test complete!]]></system-out>
        </testcase>
        <testcase name="TestAcceptanceForProvisionerResource" classname="github.com/vmware/terraform-provider-tanzu-mission-control/internal/resources/provisioner" time="29.080">
            <system-out><![CDATA[    provisioner_resource_test.go:86: provisioner resource acceptance test complete!]]></system-out>
        </testcase>
    </testsuite>

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (ee9e28b) 25.31% compared to head (25c9eca) 25.29%.

Files	Patch %	Lines
...l/resources/provisioner/data_source_provisioner.go	0.00%	2 Missing :warning:
...rnal/resources/provisioner/resource_provisioner.go	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #373 +/- ## ========================================== - Coverage 25.31% 25.29% -0.03% ========================================== Files 192 192 Lines 16665 16668 +3 ========================================== - Hits 4219 4216 -3 - Misses 12229 12234 +5 - Partials 217 218 +1 ```

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