Fix structured-lg don't work when the last line contains space

[Danieladu]

fix: #2719

[coveralls]

Pull Request Test Coverage Report for Build 83064

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 6 unchanged lines in 4 files lost coverage.
• Overall coverage remained the same at 77.264%

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Files with Coverage Reduction	New Missed Lines	%
/libraries/Microsoft.Bot.Builder.Dialogs/ObjectPath.cs	1	75.14%
/libraries/Microsoft.Bot.Builder.Dialogs/Prompts/OAuthPrompt.cs	1	57.23%
/libraries/Microsoft.Bot.Builder.Azure/CosmosDbStorageOptions.cs	2	50.0%
/libraries/Microsoft.Bot.Builder/MemoryTranscriptStore.cs	2	86.09%

Totals
Change from base Build 82934:	0.0%
Covered Lines:	7602
Relevant Lines:	9839

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💛 - Coveralls

[fuselabs]

✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.dll compared against version 4.5.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.AI.Luis.dll compared against version 4.5.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.AI.QnA.dll compared against version 4.5.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.ApplicationInsights.dll compared against version 4.5.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.Azure.dll compared against version 4.5.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.Dialogs.dll compared against version 4.5.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.TemplateManager.dll compared against version 4.5.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Configuration.dll compared against version 4.5.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Connector.dll compared against version 4.5.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Schema.dll compared against version 4.5.3