Fix tests for DataView#setFloat when no value arg is provided

Fixes gh-686

test/built-ins/DataView/prototype/setFloat32/toindex-byteoffset.js

@@ -105,4 +105,4 @@ assert.sameValue(sample.getFloat32(0), 42, "undefined");
 
 sample.setFloat32(0, 7);
 sample.setFloat32();
-assert.sameValue(sample.getFloat32(0), 0, "no arg");
+assert.sameValue(sample.getFloat32(0), NaN, "no arg");

test/built-ins/DataView/prototype/setFloat64/toindex-byteoffset.js

@@ -106,4 +106,4 @@ assert.sameValue(sample.getFloat64(0), 42, "undefined");
 
 sample.setFloat64(0, 7);
 sample.setFloat64();
-assert.sameValue(sample.getFloat64(0), 0, "no arg");
+assert.sameValue(sample.getFloat64(0), NaN, "no arg");