Remove assert preventing empty PKCS7 exports

[vcsjones]

An empty PKCS7 collection is valid, so don't require the certHandles count to be greater than 0.

Before:

DOTNET : ((null) warning) Process terminated due to " at System.Diagnostics.DebugProvider.Fail(String message, String detailMessage)
DOTNET : at System.Diagnostics.Debug.Fail(String message, String detailMessage)
DOTNET : at System.Diagnostics.Debug.Assert(Boolean condition, String message, String detailMessage)
DOTNET : at System.Diagnostics.Debug.Assert(Boolean condition)

After:

[PASS] System.Security.Cryptography.X509Certificates.Tests.CollectionTests.ExportPkcs7_Empty

[ghost]

Tagging subscribers to this area: @bartonjs, @vcsjones, @krwq, @GrabYourPitchforks
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Issue Details

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An empty PKCS7 collection is valid, so don't require the certHandles count to be greater than 0.

Before:

DOTNET : ((null) warning) Process terminated due to " at System.Diagnostics.DebugProvider.Fail(String message, String detailMessage)
DOTNET : at System.Diagnostics.Debug.Fail(String message, String detailMessage)
DOTNET : at System.Diagnostics.Debug.Assert(Boolean condition, String message, String detailMessage)
DOTNET : at System.Diagnostics.Debug.Assert(Boolean condition)

After:

[PASS] System.Security.Cryptography.X509Certificates.Tests.CollectionTests.ExportPkcs7_Empty

Author:	vcsjones
Assignees:	-
Labels:	area-System.Security, community-contribution
Milestone:	-

[ghost]

Tagging subscribers to 'arch-android': @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

Issue Details

---

An empty PKCS7 collection is valid, so don't require the certHandles count to be greater than 0.

Before:

DOTNET : ((null) warning) Process terminated due to " at System.Diagnostics.DebugProvider.Fail(String message, String detailMessage)
DOTNET : at System.Diagnostics.Debug.Fail(String message, String detailMessage)
DOTNET : at System.Diagnostics.Debug.Assert(Boolean condition, String message, String detailMessage)
DOTNET : at System.Diagnostics.Debug.Assert(Boolean condition)

After:

[PASS] System.Security.Cryptography.X509Certificates.Tests.CollectionTests.ExportPkcs7_Empty

Author:	vcsjones
Assignees:	-
Labels:	area-System.Security, os-android, community-contribution
Milestone:	-