Add fallback for invalid signature help data structure

Fixes #80617

Some extensions may provide us with bad data types (if they are js or don't have strict null enabled for example). Try to be more careful about handling such cases by falling back to an empty array instead of undefined

src/vs/workbench/api/common/extHostTypeConverters.ts

@@ -859,7 +859,7 @@ export namespace SignatureInformation {
 		return {
 			label: info.label,
 			documentation: info.documentation ? MarkdownString.fromStrict(info.documentation) : undefined,
-			parameters: info.parameters && info.parameters.map(ParameterInformation.from)
+			parameters: Array.isArray(info.parameters) ? info.parameters.map(ParameterInformation.from) : []
 		};
 	}
 
@@ -867,7 +867,7 @@ export namespace SignatureInformation {
 		return {
 			label: info.label,
 			documentation: htmlContent.isMarkdownString(info.documentation) ? MarkdownString.to(info.documentation) : info.documentation,
-			parameters: info.parameters && info.parameters.map(ParameterInformation.to)
+			parameters: Array.isArray(info.parameters) ? info.parameters.map(ParameterInformation.to) : []
 		};
 	}
 }
@@ -878,7 +878,7 @@ export namespace SignatureHelp {
 		return {
 			activeSignature: help.activeSignature,
 			activeParameter: help.activeParameter,
-			signatures: help.signatures && help.signatures.map(SignatureInformation.from)
+			signatures: Array.isArray(help.signatures) ? help.signatures.map(SignatureInformation.from) : [],
 		};
 	}
 
@@ -886,7 +886,7 @@ export namespace SignatureHelp {
 		return {
 			activeSignature: help.activeSignature,
 			activeParameter: help.activeParameter,
-			signatures: help.signatures && help.signatures.map(SignatureInformation.to)
+			signatures: Array.isArray(help.signatures) ? help.signatures.map(SignatureInformation.to) : [],
 		};
 	}
 }