Restructure `ma_log_postv` to be more consistent

The `__STDC_VERSION__ >= 199901L` and the `_MSC_VER >= 1200` code
had different styles for handling errors, so I've made them match.

miniaudio.h

@@ -8789,11 +8789,17 @@ MA_API ma_result ma_log_postv(ma_log* pLog, ma_uint32 level, const char* pFormat
             formattedLen = ma_vscprintf(&pLog->allocationCallbacks, pFormat, args2);
             va_end(args2);
 
-            if (formattedLen > 0) {
+            if (formattedLen <= 0) {
+                return MA_INVALID_OPERATION;
+            }
+
             char* pFormattedMessage = NULL;
 
             pFormattedMessage = (char*)ma_malloc(formattedLen + 1, &pLog->allocationCallbacks);
-                if (pFormattedMessage != NULL) {
+            if (pFormattedMessage == NULL) {
+                return MA_OUT_OF_MEMORY;
+            }
+
             ma_result result;
 
             /* We'll get errors on newer versions of Visual Studio if we try to use vsprintf().  */
@@ -8811,12 +8817,6 @@ MA_API ma_result ma_log_postv(ma_log* pLog, ma_uint32 level, const char* pFormat
             ma_free(pFormattedMessage, &pLog->allocationCallbacks);
 
             return result;
-                } else {
-                    return MA_OUT_OF_MEMORY;
-                }
-            } else {
-                return MA_INVALID_OPERATION;
-            }
         }
         #else
         {