fix(oracle): require vault conversion not zero

Author: Rubilmax

src/ChainlinkOracle.sol

@@ -59,6 +59,7 @@ contract ChainlinkOracle is IOracle {
         require(
             address(vault) != address(0) || vaultConversionSample == 1, ErrorsLib.VAULT_CONVERSION_SAMPLE_IS_NOT_ONE
         );
+        require(vaultConversionSample != 0, ErrorsLib.VAULT_CONVERSION_IS_ZERO);
 
         VAULT = vault;
         VAULT_CONVERSION_SAMPLE = vaultConversionSample;

src/libraries/ErrorsLib.sol

@@ -9,6 +9,9 @@ library ErrorsLib {
     /// @notice Thrown when the answer returned by a Chainlink feed is negative.
     string constant NEGATIVE_ANSWER = "negative answer";
 
+    /// @notice Thrown when the vault conversion sample is 0.
+    string constant VAULT_CONVERSION_SAMPLE_IS_ZERO = "vault conversion sample is zero";
+
     /// @notice Thrown when the vault conversion sample is not 1 while vault = address(0).
     string constant VAULT_CONVERSION_SAMPLE_IS_NOT_ONE = "vault conversion sample is not one";
 }