Don't use exceptions for time zones (case 1100856)

The current class library code uses managed exceptions for flow control
for time zone handling. Specifically, it depends on exceptions to occur
if one of the files that _might_ have time zone information does not
exist.

On Android with IL2CPP we run into problems with C++ exceptions causing
hangs in some cases. Since IL2CPP implements managed exceptions using
C++ exceptions, this code can cause problems.

This change corrects Unity case 1100856.

Author: Josh Peterson

mcs/class/corlib/System/TimeZoneInfo.cs

@@ -209,7 +209,8 @@ static TimeZoneInfo CreateLocal ()
 					string tzName = null;
 					if (!TryGetNameFromPath (tzFilePath, out tzName))
 						tzName = "Local";
-					return FindSystemTimeZoneByFileName (tzName, tzFilePath);
+					if (File.Exists(tzFilePath))
+						return FindSystemTimeZoneByFileName (tzName, tzFilePath);
 				} catch (TimeZoneNotFoundException) {
 					continue;
 				}
@@ -1561,4 +1562,4 @@ public override string ToString ()
 	}
 #endif
 	}
-}
+}