bench: fix NaN check to use imaginary part

---
type: pre_commit_static_analysis_report
description: Results of running static analysis checks when committing changes.
report:
  - task: lint_filenames
    status: passed
  - task: lint_editorconfig
    status: passed
  - task: lint_markdown
    status: na
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    status: na
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    status: na
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    status: na
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    status: na
  - task: lint_c_src
    status: na
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  - task: lint_typescript_tests
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    status: passed
---

Author: anandkaranubc

lib/node_modules/@stdlib/math/base/special/cflipsign/benchmark/benchmark.native.js

@@ -26,6 +26,7 @@ var uniform = require( '@stdlib/random/base/uniform' );
 var isnan = require( '@stdlib/math/base/assert/is-nan' );
 var Complex128 = require( '@stdlib/complex/float64/ctor' );
 var real = require( '@stdlib/complex/float64/real' );
+var imag = require( '@stdlib/complex/float64/imag' );
 var tryRequire = require( '@stdlib/utils/try-require' );
 var pkg = require( './../package.json' ).name;
 
@@ -50,7 +51,6 @@ bench( pkg+'::native', opts, function benchmark( b ) {
 		new Complex128( uniform( -500.0, 500.0 ), uniform( -500.0, 500.0 ) ),
 		new Complex128( uniform( -500.0, 500.0 ), uniform( -500.0, 500.0 ) )
 	];
-
 	v = uniform( -500.0, 500.0 );
 
 	b.tic();
@@ -61,7 +61,7 @@ bench( pkg+'::native', opts, function benchmark( b ) {
 		}
 	}
 	b.toc();
-	if ( isnan( real( y ) ) ) {
+	if ( isnan( imag( y ) ) ) {
 		b.fail( 'should not return NaN' );
 	}
 	b.pass( 'benchmark finished' );