[VitisAI][Fix] ShapeInferContext GetAttrxxxs support empty value (microsoft#21471)

### Description
Bug fix for the ShapeInferContext GetAttrxxxs APIs. Node attribute maybe
is empty.



### Motivation and Context
If the attr value is empty, the expected result through the interface is
empty , but currently, it returns a meaningless {0}.

---------

Co-authored-by: mingyue <mingyue@amd.com>
Co-authored-by: Liu Minyue <mingyue@xilinx.com>

Author: mingyueliuh

include/onnxruntime/core/session/onnxruntime_cxx_inline.h

@@ -2044,13 +2044,19 @@ inline ShapeInferContext::Ints ShapeInferContext::GetAttrInts(const char* attr_n
   int64_t i = {};
   size_t out = {};
   // first call to get the bytes needed
+  // 1. A status == nullptr means that ReadOpAttr was successful. A status != nullptr means failure.
+  // 2. The ReadOpAttr function should normally be called twice: once to get the needed buffer size (returns a status != nullptr), and a second time to actually read the ints (returns status == null on success).
+  // 3. This code tries a subtle optimization in the first call to ReadOpAttr. It passes in a buffer (&i) of size 1 just in case there is only 1 int. In this case, status == nullptr and we need to return {i}.
   auto status = ort_api_->ReadOpAttr(attr, ORT_OP_ATTR_INTS, &i, sizeof(i), &out);
   if (status) {
     size_t num_i = out / sizeof(int64_t);
     ShapeInferContext::Ints ints(num_i, 0);
     Ort::ThrowOnError(ort_api_->ReadOpAttr(attr, ORT_OP_ATTR_INTS, ints.data(), out, &out));
     return ints;
   } else {
+    if (out == 0u) {
+      return {};
+    }
     return {i};
   }
 }
@@ -2068,13 +2074,19 @@ inline ShapeInferContext::Floats ShapeInferContext::GetAttrFloats(const char* at
   float f = {};
   size_t out = {};
   // first call to get the bytes needed
+  // 1. A status == nullptr means that ReadOpAttr was successful. A status != nullptr means failure.
+  // 2. The ReadOpAttr function should normally be called twice: once to get the needed buffer size (returns a status != nullptr), and a second time to actually read the ints (returns status == null on success).
+  // 3. This code tries a subtle optimization in the first call to ReadOpAttr. It passes in a buffer (&i) of size 1 just in case there is only 1 int. In this case, status == nullptr and we need to return {i}.
   auto status = ort_api_->ReadOpAttr(attr, ORT_OP_ATTR_FLOATS, &f, sizeof(f), &out);
   if (status) {
     size_t num_f = out / sizeof(float);
     ShapeInferContext::Floats floats(num_f, 0);
     Ort::ThrowOnError(ort_api_->ReadOpAttr(attr, ORT_OP_ATTR_FLOATS, floats.data(), out, &out));
     return floats;
   } else {
+    if (out == 0u) {
+      return {};
+    }
     return {f};
   }
 }
@@ -2099,6 +2111,9 @@ inline ShapeInferContext::Strings ShapeInferContext::GetAttrStrings(const char*
   char c = {};
   size_t out = {};
   // first call to get the bytes needed
+  // 1. A status == nullptr means that ReadOpAttr was successful. A status != nullptr means failure.
+  // 2. The ReadOpAttr function should normally be called twice: once to get the needed buffer size (returns a status != nullptr), and a second time to actually read the ints (returns status == null on success).
+  // 3. This code tries a subtle optimization in the first call to ReadOpAttr. It passes in a buffer (&i) of size 1 just in case there is only 1 int. In this case, status == nullptr and we need to return {i}.
   auto status = ort_api_->ReadOpAttr(attr, ORT_OP_ATTR_STRINGS, &c, sizeof(char), &out);
   if (status) {
     std::vector<char> chars(out, '\0');
@@ -2115,6 +2130,9 @@ inline ShapeInferContext::Strings ShapeInferContext::GetAttrStrings(const char*
     }
     return strings;
   } else {
+    if (out == 0u) {
+      return {};
+    }
     return {std::string{c}};
   }
 }