Check partial conversion on FP16 to FP32 AVX Cast kernel (#22091)

### Description
Added checks to convert partial vectors in the early stages of the FP16
to FP32 cast using AVX NE CONVERT ISA.



### Motivation and Context
Avoid storing data in sections outside of the output buffer, these
checks are missing on the [original
PR](https://github.com/microsoft/onnxruntime/pull/21183).
This fix prevents memory corruption when the output buffer has a size
[n*16 + 1, n*16 + 7] with 0< n

onnxruntime/core/mlas/lib/amd64/cvtfp16Avx.asm

@@ -54,7 +54,7 @@ HIGH_SELECTOR   equ 00110001b
 
 LEAF_ENTRY MlasCastF16ToF32KernelAvx, _TEXT
 
-	test    r8, r8                  ; Check if we have any elements to convert
+    test    r8, r8                  ; Check if we have any elements to convert
     jz      ExitRoutine
     cmp     r8, 8
     jb      ConvertMaskedVectors
@@ -80,6 +80,8 @@ Convert256Vectors:
         jz      ExitRoutine ; If we are done, exit
         cmp     r8, 16      ; If the vector is big enough, we go again
         jae     Convert256Vectors
+        cmp     r8, 8       ; Check if we have enough elements to convert
+        jb      ConvertMaskedVectors
 
 
 

onnxruntime/core/mlas/lib/x86_64/cvtfp16Avx.S

@@ -51,8 +51,6 @@ FUNCTION_ENTRY MlasCastF16ToF32KernelAvx
 
         test    rdx, rdx      // Check if we have any elements to convert
         jz      ExitRoutine
-
-AVX_NE_CONVERT:
         cmp     rdx, 8
         jb      ConvertMaskedVectors
         cmp     rdx, 16
@@ -75,6 +73,8 @@ Convert256Vectors:
         jz      ExitRoutine     // If we are done, exit
         cmp     rdx, 16         // If the vector is big enough, we go again
         jae     Convert256Vectors
+        cmp	rdx, 8           // Check if we have enough elements to convert
+        jb      ConvertMaskedVectors