ICU-21502 Adds status checks to test to prevent segementation fault when
test runs with ICU stub data only.

ICU-21502 Review comments worked in.
diff --git a/icu4c/source/test/intltest/units_test.cpp b/icu4c/source/test/intltest/units_test.cpp
index 3a8522b..a18e751 100644
--- a/icu4c/source/test/intltest/units_test.cpp
+++ b/icu4c/source/test/intltest/units_test.cpp
@@ -708,10 +708,26 @@
 
     for (const auto &testCase : testCases) {
         MeasureUnitImpl inputImpl = MeasureUnitImpl::forIdentifier(testCase.input, status);
+        if (status.errIfFailureAndReset()) {
+            continue;
+        }
         MeasureUnitImpl outputImpl = MeasureUnitImpl::forIdentifier(testCase.output, status);
+        if (status.errIfFailureAndReset()) {
+            continue;
+        }
         ComplexUnitsConverter converter(inputImpl, outputImpl, conversionRates, status);
+        if (status.errIfFailureAndReset()) {
+            continue;
+        }
 
         auto actual = converter.convert(testCase.inputValue, nullptr, status);
+        if (status.errIfFailureAndReset()) {
+            continue;
+        }
+        if (actual.length() < testCase.expectedCount) {
+            errln("converter.convert(...) returned too few Measures");
+            continue;
+        }
 
         for (int i = 0; i < testCase.expectedCount; i++) {
             assertEquals(testCase.msg, testCase.expected[i].getUnit().getIdentifier(),