ICU-20392 Bugfix: Don't access old std::variant<> data after emplace().

This just happens to work a lot of the time but it isn't correct.

Author: roubert

icu4c/source/common/locid.cpp

@@ -1994,21 +1994,20 @@ Locale& Locale::init(StringPiece localeID, UBool canonicalize)
             U_ASSERT(fullNameBuffer.isEmpty());
             nest.init(language, script, region, variantBegin);
         } else {
-            std::unique_ptr<Heap>& heap = payload.emplace<std::unique_ptr<Heap>>(
-                std::make_unique<Heap>(language, script, region, variantBegin));
-            if (!heap) {
-                break; // error: out of memory
-            }
             if (fullName == nest.baseName) {
                 U_ASSERT(fullNameBuffer.isEmpty());
-                heap->fullName = {fullName, static_cast<std::string_view::size_type>(length)};
-                if (heap->fullName.isEmpty()) {
+                fullNameBuffer = {fullName, static_cast<std::string_view::size_type>(length)};
+                if (fullNameBuffer.isEmpty()) {
                     break; // error: out of memory
                 }
-            } else {
-                U_ASSERT(!fullNameBuffer.isEmpty());
-                heap->fullName = std::move(fullNameBuffer);
             }
+            std::unique_ptr<Heap>& heap = payload.emplace<std::unique_ptr<Heap>>(
+                std::make_unique<Heap>(language, script, region, variantBegin));
+            if (!heap) {
+                break; // error: out of memory
+            }
+            U_ASSERT(!fullNameBuffer.isEmpty());
+            heap->fullName = std::move(fullNameBuffer);
         }
 
         initBaseName(err);