Fix constructor bug in mixed_vector

paddle/fluid/framework/mixed_vector.h

@@ -37,9 +37,8 @@ class Vector {
 
   // Fill vector with value. The vector size is `count`.
   explicit Vector(size_t count, const T& value = T()) {
-    if (count == 0) {
-      InitEmpty();
-    } else {
+    InitEmpty();
+    if (count != 0) {
       resize(count);
       T* ptr = begin();
       for (size_t i = 0; i < count; ++i) {

paddle/fluid/framework/mixed_vector_test.cu

@@ -15,6 +15,7 @@
 
 #include "glog/logging.h"
 #include "gtest/gtest.h"
+#include "mixed_vector.h"
 #include "paddle/fluid/framework/mixed_vector.h"
 #include "paddle/fluid/platform/gpu_info.h"
 
@@ -91,3 +92,10 @@ TEST(mixed_vector, MultiGPU) {
     ASSERT_EQ(tmp[i], i * 100);
   }
 }
+
+TEST(mixed_vector, InitWithCount) {
+  paddle::framework::Vector<int> vec(10, 10);
+  for (int i = 0; i < 10; ++i) {
+    ASSERT_EQ(vec[i], 10);
+  }
+}