Prevent mipmapping of 1x1 textures.

In Metal, if a texture has all dimensions being a single texel big the mipmapping call `generateMipmapsForTexture` will fail and throw an exception.  So we add a check to the existing one in `HgiMetalBlitCmds::GenerateMipMaps()` which catches this.

Thanks to @Morteeza for this.

Contribution: Apple

Fixes #2264

(Internal change: 2281900)

pxr/imaging/hgiMetal/blitCmds.mm

@@ -444,29 +444,46 @@
 }
 
 static bool
-_HgiCanBeFiltered(HgiFormat format)
+_HgiTextureCanBeFiltered(HgiTextureDesc const &descriptor)
 {
-    HgiFormat const componentFormat = HgiGetComponentBaseFormat(format);
+    HgiFormat const componentFormat =
+        HgiGetComponentBaseFormat(descriptor.format);
 
-    switch(componentFormat) {
-    case HgiFormatInt16:
-    case HgiFormatUInt16:
-    case HgiFormatInt32:
+    if (componentFormat == HgiFormatInt16 ||
+        componentFormat == HgiFormatUInt16 ||
+        componentFormat == HgiFormatInt32) {
         return false;
-    default:
-        return true;
     }
+
+    GfVec3i const dims = descriptor.dimensions;
+    switch (descriptor.type) {
+        case HgiTextureType1D:
+        case HgiTextureType1DArray:
+            return (dims[0] > 1);
+
+        case HgiTextureType2D:
+        case HgiTextureType2DArray:
+            return (dims[0] > 1 || dims[1] > 1);
+
+        case HgiTextureType3D:
+            return (dims[0] > 1 || dims[1] > 1 || dims[2] > 1);
+
+        default:
+            TF_CODING_ERROR("Unsupported HgiTextureType enum value");
+            return false;
+    }
+
+    return false;
 }
 
 void
 HgiMetalBlitCmds::GenerateMipMaps(HgiTextureHandle const& texture)
 {
     HgiMetalTexture* metalTex = static_cast<HgiMetalTexture*>(texture.Get());
+
     if (metalTex) {
-        HgiFormat const format = metalTex->GetDescriptor().format;
-        if (_HgiCanBeFiltered(format)) {
+        if (_HgiTextureCanBeFiltered(metalTex->GetDescriptor())) {
             _CreateEncoder();
-            // Can fail if the texture format is not filterable.
             [_blitEncoder generateMipmapsForTexture:metalTex->GetTextureId()];
         }
     }