deadlock fix

Author: Artem Ermoshkin

include/ydb-cpp-sdk/client/iam/common/generic_provider.h

@@ -168,7 +168,6 @@ class TGrpcIamCredentialsProvider : public ICredentialsProvider {
                     }
                 };
                 auto facility = weakFacility.lock();
-                auto self = weakSelf.lock();
 
                 try {
                     if (facility) {
@@ -178,7 +177,7 @@ class TGrpcIamCredentialsProvider : public ICredentialsProvider {
                 } catch (...) {
                 }
 
-                if (self) {
+                if (auto self = weakSelf.lock()) {
                     std::lock_guard guard(self->Lock_);
                     self->ResetContextImpl();
                 }